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An Introduction To Geology | by William B. Scott



This book had its origin in the attempt to write an introductory work, dealing principally with American Geology, upon the lines of Sir Archibald Geikie's excellent little " Class-Book." In spite of vigorous efforts at compression, it has expanded to its present size, though the difference from the "Class-Book," in this respect, lies not so much in the quantity of matter as in the larger size of the type and illustrations.

TitleAn Introduction To Geology
AuthorWilliam B. Scott
PublisherThe Macmillan Company
Year1921
Copyright1907, The Macmillan Company
AmazonAn Introduction to Geology

Second Edition Revised Throughout

By William B. Scott, Ph.D., LL.D, Blair Professor Of Geology And Palaeontology In Princeton University.

"There rolls the deep where grew the tree. O earth what changes hast thou seen! There where the long street roars, hath been The stillness of the central sea.

" The hills are shadows, and they flow.

From form to form and nothing stands; They melt like mists, the solid lands, Like clouds they shape themselves and go".

Tennyson.

With numerous illustrations from drawings by Bruce Horsfall and from many new photographs.

This Book is Dedicated In Grateful Recognition Of An Ever Ready And Inspiring Sympathy

-From The Preface To The First Edition
This book had its origin in the attempt to write an introductory work, dealing principally with American Geology, upon the lines of Sir Archibald Geikie's excellent little Class-Book. In spite of v...
-Preface To The Second Edition
The ten years that have passed since the first publication of this book have been years fruitful of results in geological knowledge. Some departments of the subject have been fairly revolutionized and...
-Introduction
Geology is the study of the structure, history, and development of the earth and its inhabitants, as revealed in the rocks. From this definition it is apparent that the central problem in geology i...
-Introduction. Continued
Geology is a unit and, though for the purpose of orderly treatment, it is necessary to divide the subject into various provinces, it should be clearly understood that these provinces are rather the va...
-Chapter A. The Rock-Forming Minerals
Of the simple undecomposable substances which chemists call elements, and of which rather more than seventy have been discovered, only sixteen enter at all largely into the composition of the earth's ...
-The Rock-Forming Minerals. Continued
Forms And Combinations A form is an assemblage of faces, all of which have similar relations to the axes. Two or more forms occurring as a single crystal constitute a combination. Only forms belong...
-A. Minerals Composed Of Silica
Next to oxygen, silicon is by far the most abundant constituent of the earth's crust, though never occurring alone. It is united with oxygen to form silica (Si02) or enters into the formation of more ...
-B. Minerals Composed Of Silicates. I. The Felspar Group
There are several silicic acids, which form a very extensive series of compounds with various metallic bases. As rock-forming minerals the silicates are of the first importance. The felspars are es...
-II. The Felspathoid Group
These minerals are very closely allied to the felspars in chemical composition and geological relations, but differ from them in crystal form and physical properties. They have a much more restricted ...
-III. The Mica Group
These minerals have a complex chemical composition, and are so variable that it is difficult to give formulae for them; they are silicates of alumina, together with potash, lithia, magnesia, iron, or ...
-IV. The Amphibole And Pyroxene Groups
These two groups contain parallel series of minerals of similar chemical composition, but differing in their crystallization and physical properties. In composition they range from silicates of magnes...
-V. The Olivine Group
Olivine is the only mineral of this group of sufficient importance to require mention; it is a silicate of magnesia and iron, 2(Mg, Fe)0 Si02, though the percentage of iron varies greatly. Sp. gr. =3....
-C. Other Silicates, Chiefly Decomposition Products
Many of the complex silicates, when long exposed to the action of the weather and of percolating waters, become more or less c profoundly changed chemically, a change which is known as alteration and ...
-II. Talc And Chlorite Groups
1. Chlorite Under this name are grouped a number of closely allied minerals, which are hydrated silicates of alumina, magnesia, and iron. They are soft minerals, with a hardness of 1-1.5 and a spec...
-D. Calcareous Minerals
1. Calcite Calcite, carbonate of lime, CaC03. Sp. gr. = 2.72; H=3-This mineral crystallizes in the hexagonal system, in a great variety of forms; rhombohedrons and scalenohedrons are common; hexago...
-E. Iron Minerals
1. Haematite Haematite, or Specular Iron, is ferric oxide, Fe203. Sp. gr. = 4.5-5.3; H = 6.5. Crystallizes in rhombohedrons, or more commonly, in nodular masses. The colour is black, steel-grey, or...
-Part I. Dynamical Geology
We have already seen that the chief task of geology is to construct a history of the earth, to determine how and in what order the rocks were formed, through what changes they have passed, and how the...
-Section I. Subterranean Or Igneous Agencies. Chapter I. Diastrophism. Earthquakes
The subterranean agencies are those which are due to the earth's own inherent energy and arise deep within the earth's interior, though they are often displayed at the surface in a most striking manne...
-Evidences Of Elevation
On certain coasts long inhabited by civilized man, ancient structures like quays and bridges, which were built in the water, may now be found high above it. Such changes have been noted in the Mediter...
-Evidences Of Depression
As ancient structures on long-inhabited coasts sometimes show elevation, they likewise sometimes show depression. On the north coast of Egypt ancient rock-cut tombs are now visible beneath the waters ...
-Earthquakes
An earthquake is caused by a series of elastic waves due to a sudden shock in the earth's interior; the visible phenomena at the surface are produced by the outcropping of these waves and by the movem...
-Distribution Of Earthquakes
Sensible earthquakes are very numerous, not less than 30,000 is the estimated number per annum; of course, the great majority of these are very light. While any part of the earth's surface may be visi...
-Classification Of Earthquakes
Earthquakes may be classified in several ways, according to the purpose in view. With regard to the manner of production, they may be grouped into volcanic and tectonic quakes, which will be explained...
-Phenomena Of Earthquakes
The phenomena of earthquakes differ greatly in accordance with the number, duration, and intensity of the shocks, and with the distance of the place of observation from that of the origin of the distu...
-Effects Of Earthquakes
Strictly speaking, the geological effects of earthquakes are of less importance than is usually supposed. The violent shaking of the surface often brings about great land-slips in mountain regions, wh...
-Causes Of Earthquakes
In respect to their mode of causation, earthquakes are usually divided into two classes, volcanic and tectonic, though it is often impossible to determine to which of the two classes a given earthquak...
-Chapter II. Volcanoes
A volcano is usually a conical mountain or hill, with an opening, or crater, through which various solid, molten, or gaseous materials are ejected. The essential part of the volcano is the opening, or...
-Volcanic Eruptions
The phenomena displayed by different volcanoes, or even by the same volcano at different times, vary greatly. It often seems difficult to believe that similar forces are involved, and that the diverge...
-Volcanic Eruptions. Continued
The year 1902 was made memorable by a series of excessively violent explosive eruptions, in some instances accompanied by frightful destruction and loss of life, in Central America and the Lesser Anti...
-New Volcanoes
During historic times a considerable number of new volcanoes have been formed, both on land and in the bed of the sea, the latter resulting in the birth of new islands. Aside from certain newly formed...
-Chapter III. Volcanoes. Internal Constitution Of The Earth. Volcanic Products
These form the most important part of the subject from the geological point of view, because they contribute largely to the permanent materials of the earth's crust. We meet with such materials of all...
-(1) Lava
A lava is a more or less completely melted rock; the degree of fluidity varies greatly in different lavas, but is rarely, if ever, perfect. Instead of being a true liquid, a lava ordinarily consists o...
-Lava. Continued
Large crystals are, it is true, very often found in lavas, but these were formed before the ejection of the mass from the volcano. Such crystals frequently contain enclosures of glass, which indicate ...
-(2) Fragmental Products
This division includes all the materials which are ejected from the volcano in a solid state. These are of all sizes and shapes, from huge blocks weighing many tons, down to the most impalpable dust, ...
-(3) The Gaseous Products
The Gaseous Products are important as agents of the eruptions, in promoting the crystallizing of the lavas, and in altering the rocks with which they come in contact. The most abundant is steam. Carbo...
-Volcanic Cones
Volcanic Cones are built up by the material which the volcanoes eject, and vary in shape according to the character of those materials and to the violence of the eruptions. Those vents which yield onl...
-Fissure Eruptions
There is much reason to believe that the mode of volcanic eruption from a single vent, described in the foregoing pages, is not the only method by which molten lava may reach the surface. It would see...
-The Causes Of Volcanic Activity
Many theories have been advanced to explain the causes of vulcanism, but, it must be candidly admitted, none of them is satisfactory. In an elementary book, like this, no adequate discussion of this m...
-(2) The High Temperature
The High Temperature has been explained in two principal ways. If we accept the nebular hypothesis of the origin of the Solar System, we must grant that the earth was once a globe of glowing gas, whic...
-(4) The Causes Of The Ascensive Force Of The Lava Column
The Causes Of The Ascensive Force Of The Lava Column are sought by various writers in several different agencies. Some find an all-sufficient cause in the steam pressure, while others maintain that so...
-The Internal Constitution Of The Earth
The interior of the earth is completely beyond the reach of direct observation and what is known, or may be reasonably inferred, as to its physical constitution, is derived from various lines of indir...
-Temperature Of The Earth's Interior
Volcanoes, which eject molten and white-hot lavas, and thermal springs, which pour out floods of hot and even boiling water, plainly indicate that the interior of the earth is highly heated, at least ...
-Physical State Of The Earth's Interior
Opinions concerning the internal constitution of the earth differ very radically and only within the last few years has evidence begun to accumulate which permits the drawing of certain inferences wit...
-Summary
The study of the subterranean, or igneous, agencies has proved to be very unsatisfactory in the way of explaining the phenomena and referring them to the operation of understood physical agents, becau...
-Section II. Surface Agencies
The superficial, or surface, agents, all of which are manifestations of solar energy, are those which act upon or near the surface of the ground; only one, circulating water, is able to penetrate to c...
-Chapter IV. Destructive Processes - The Atmosphere
The atmospheric agencies are by far the most important of the destructive or denuding agents, because no part of the land surface is altogether exempt from their activity. Their work is described by t...
-1. Rain
The work of the rain, which is both chemical and mechanical, varies greatly in accordance with climatic factors. The annual precipitation of two regions may be the same in amount, but in one the rainf...
-Rain. Part 2
In most tropical regions, where there is a long dry season, followed by a wet season of violent rainfall, the manner of decay is characteristically different. The felspars and other aluminous silicate...
-Rain. Part 3
Other things being equal, the rapidity with which the rain sweeps away the soil depends upon the steepness of the slope upon which the soil is formed; for gravity largely determines these movements. O...
-2. Frost
The term frost, in this connection, is restricted to the freezing of water. Water is one of the comparatively few substances which expand considerably on solidifying. This expansion amounts to about o...
-3. Changes Of Temperature
In moist and equable climates these temperature changes are of very subordinate importance as a destructive agent and act chiefly in giving an easier passage to percolating waters. In arid regions, on...
-4. Wind
The wind, of itself and unassisted by hard particles, can accomplish but little in disintegrating firm rocks, but on high mountain crests and knife-edges, where the wind blows with great velocity, i...
-Chapter V. Destructive Processes. - Running Water
The source of all running water, whether surface or underground, is atmospheric precipitation. All springs and streams are merely rain (or snow) water collected and fed from reservoirs. The rain-water...
-1. The Ground Water
Within the soil the movement of water is in different directions according to circumstances. In climates of considerable rainfall which have no long dry season, the movement is chiefly downward, due t...
-2. Springs
Springs are the openings of the ground water upon the surface, and could not be formed were the land perfectly free from irregularities, for gravity controls the movement of underground waters, and th...
-3. Rivers. Erosion By Rivers
The destructive work of rivers, including in that term all surface streams, is far less extensive, in the aggregate, than that of the atmospheric agencies, but because the work of a stream is concentr...
-Erosion By Rivers. Continued
Unless the region through which a river flows is upheaved, and thus, by increasing the fall, renewed power is given to the stream, a stage must sooner or later be reached when the vertical cutting of ...
-Materials Mechanically Carried
The transporting power of running water is dependent upon the velocity of the current, and both mathematical and experimental treatment of the problem brings out the surprising result that the transpo...
-Materials In Solution
In addition to what the river carries down mechanically in suspension or sweeps along the bottom, there is a third class of material; namely, that which is dissolved in the waters of the stream. Disso...
-Chapter VI. Destructive Processes. - Snow And Ice, The Sea, Lakes, Animals And Plants
Avalanches are great masses of snow which descend from the mountain tops at a very high velocity, and are frequent in all high mountains with heavy snowfall, and occur, though less commonly, on mounta...
-Snow And Ice, The Sea, Lakes, Animals And Plants as Destructive Processes. Part 2
The structure of glacial ice is characteristically different from that produced by the freezing of a body of water. The latter is made up of parallel crystals with optical axes perpendicular to the su...
-Snow, Ice, The Sea, Lakes, Animals And Plants as Destructive Processes. Part 3
This is a type of especial interest and significance to the geologist, because of the light which it throws upon the often mysterious operations of the ice-sheets which once covered large portions of ...
-Glacier Transportation
The transporting power of a glacier is' not determined by its velocity, at least so far as the material carried on its surface is concerned. This is because the rocks may be regarded as floating bodie...
-2. The Sea
The destructive work of the sea is accomplished mainly by means of the waves which the wind raises upon its surface and by wind and tidal currents. The great ocean currents are, as a rule, so far from...
-3. Lakes
In comparison with the long life of the earth, lakes must be regarded as merely temporary bodies of water, which will sooner or later disappear, either by being drained of their waters or by being fil...
-4. Organic Agencies
The organic agencies are animals and plants, both living and after death. In some respects these agencies tend to counteract the destructiveness of others, and the protective effects may be taken up f...
-Chapter VII. Reconstructive Processes. - Continental Deposits, Land, Swamp, And River
We have now to inquire what becomes of the material which is derived from the decomposition and disintegration of the rocks. At the present time, it is estimated, about one-half of the waste of the la...
-Stratification
It is an almost universal characteristic of sedimentary accumulations, whether modern deposits or ancient rocks, that they are stratified, that is, divided into more or less parallel layers or beds. I...
-A. Continental Deposits
The continental deposits may be classified in several different ways, each one of which has its advantages according to the object aimed at. Our present purpose will best be served by arranging these ...
-1. Terrestrial Deposits
Under this head are included those accumulations of the mechanical and chemical waste of preexistent rocks which are formed on land surfaces and not in permanent bodies of water. Deposits made by ice ...
-Residual Accumulations; Soil
As we have already seen, the disintegration and decay of rock results in the formation of soil, which is the residuum after the removal of more or less of the parent rock:. In humid climates there is...
-Chemical Deposits
In the tropics, which so largely have a regular alternation of rainy and dry seasons, and in arid regions, where the rain often falls in torrential showers, followed by long periods of drought, the mo...
-Loess
Fig. 84. - Loess deposits; North China. (Photograph by Willis). In arid regions the wind often carries the finer parts of the soil to immense distances and deposits them where they are less exp...
-Blown Sand
Wherever a sandy soil occurs unprotected by vegetation, as in deserts or along the seacoast, the wind drifts the sand and piles it up into hills or sand dunes. The dunes are roughly divided into layer...
-Spring Deposits
As our knowledge of microscopic plants increases, many processes which were believed to be purely chemical, are found to be dependent upon the activity of minute plants. At present, it is not possible...
-Cave Deposits
The chemically formed cave deposits are due to the solution and redeposition of carbonate of lime. Caves are very generally found in limestones, and the percolating waters which make their way through...
-II. Palustrine Or Swamp Deposits
The most important of the swamp and bog deposits are the vegetable accumulations, for the preservation of which a certain amount of water is necessary. The vast quantities of coal which occur in so ma...
-III. Fluviatile Or River Deposits
In a preceding chapter we learned that the power of a stream of water to transport sediment depends upon its velocity, which, in its turn, is determined by the slope of the ground and the volume of wa...
-Alluvial Cones Or Fans
Where a swift torrent, descending a steep slope, debouches on a plain or wide valley, its velocity is greatly diminished, and a large part of the material which it carries is thrown down and spread in...
-Flood Plains
Rivers, as is well known, are subject to floods when the volume of water is enormously increased and can no longer be contained in the ordinary channel, but spreads out over the level ground on each s...
-River Terraces And Old Gravels
The lower courses of many rivers, including most of those in the northern United States, and some in the southern, are bordered by a succession of terraces that rise symmetrically on the two sides of ...
-Deltas
Deltas are accumulations of river deposits at the mouths of streams, land areas which the rivers have recovered from the body of water into which they flow. The factors which determine the formation o...
-Chapter VIII. Reconstructive Processes. - Continental Deposits, Lake And Ice. IV. Lacustrine Or Lake Deposits
The term lake is a comprehensive one and includes all continental bodies of water, not in tidal communication with the sea, in which the water is relatively stationary and not actively running like a ...
-1. Fresh-Water Lakes, A. Mechanical Deposits
The mechanical sediment which accumulates in a lake basin is of two kinds, (1) that which is brought in by tributary streams, and (2) that which the lake itself acquires by cutting back its shores; of...
-C. Organic Deposits
Organic Deposits are seldom important in large lakes, but often decidedly so in small ones. As we have already seen, peat often forms to such an extent as to choke up the lake and convert it into a bo...
-2. Salt Lakes
Salt Lakes are especially characteristic of arid climates, in which the rainfall is light and evaporation great. They may be formed in either of two ways: (1) through the separation of bodies of water...
-The Chemical Deposits
The Chemical Deposits are much the most interesting and characteristic of the accumulations gathered in salt lakes. These chemical precipitates differ much in the various lakes, according to the natur...
-V. Ice Deposits
Deposits made, directly or indirectly, by the agency of ice are very characteristic, and though some are formed on land and some under water, it is desirable to consider them together in a single sect...
-Glacial Deposits
We have already learned that glaciers carry with them great masses of debris, either in the form of lateral and medial moraines upon their upper surfaces, or frozen in the interior of the ice, or push...
-Iceberg Deposits
When a glacier flows into the sea great masses are broken off from the foot and float away as icebergs. Icebergs are thus seen to be, as indeed they always are, derived from land ice and not from the ...
-Coast Ice Deposits
In high latitudes with intensely cold winters, great fields of ice (the ice-foot) are formed by the freezing of sea-water along the shore. The ice-foot becomes loaded with great masses of rock, part o...
-Climatic Relations Of Continental Deposits
This subject, though of great importance in deciphering the earth's history, is extremely complex and can be but briefly outlined here. Fig. 123. - Deposit partly made by strandad ice, west coa...
-Chapter IX. Reconstructive Processes. - Marine And Estuarine Deposits. B. Marine Deposits
The sea is the great theatre of sedimentary accumulation, and rocks of marine origin form the larger part of the present land surfaces. Important as other classes of deposits may be, they are less so ...
-I. Littoral Deposits
Littoral Deposits are laid down between low and high-water marks, and by heavy storms and exceptional tides, somewhat above the former. Thus, the accumulations of this class grade into continental dep...
-2. Shoal-Water Deposits
The material of the littoral zone is continued out beyond low-water mark to distances which vary according to several circumstances. Where, for long distances, no large rivers enter the sea and the ma...
-Limestone Banks
In favourable situations immense submarine plateaus or banks are built up in shallow waters by the accumulated remains of all sorts of lime-secreting animals, corals, echinoderms, molluscs, worms, and...
-Corals
The animals of this group show great variety of form, size, and habit of growth, and by no means all of them are important as rock-makers. The solitary corals, which are widely distributed, even in th...
-3. Aktian Deposits
The 100-fathom line is by Murray and Renard regarded as the boundary between shallow and deep water, for it generally marks the edge of the continental shelf, from which the bottom rises very gently t...
-4. The Abysmal Deposits
The Abysmal Deposits are those the materials of which are not directly derived from the land, but consist of matters carried to the sea in solution and extracted from the sea-water by the agency of or...
-Climatic Relations Of Marine Deposits
The shoal-water deposits of cold and temperate seas are much alike, both having a preponderance of sand and gravel, with occasional limestones which are more frequent in lower latitudes, while in the ...
-Estuarine Deposits
An estuary is a wide opening at the mouth of a river into which the sea has penetrated by the depression of the land. In such bodies of water the tide often scours with much force. Estuaries abound al...
-The Consolidation Of Sediments (Diagenesis)
The processes of deposition upon the land and beneath the water, which we have so far been studying, result, for the most part, only in the bringing together of great masses of loose and incoherent ma...
-Summary Of The Reconstructive Processes
The destructive agencies supply a great mass of material, of which, under existing conditions of climate, topography, etc., about one-half is arrested in its journey to the sea and the remaining half ...
-Part II. Structural Or Tectonic Geology. Chapter X. The Rocks Of The Earth's Crust - Igneous Rocks
In the first section of this book we made a study of the processes and agencies which are still at work upon and within the earth, tending to modify it in one or other particular. We there found that ...
-Rocks
The distinction between a rock and a mineral is not always an easy one for the beginner to grasp, yet it is essential that he should do so. A Rock is any extensive constituent of the earth's crust, wh...
-Igneous Rocks
The igneous rocks have a deep-seated origin and have either forced their way to the surface, or have cooled and solidified at varying depths beneath it. Though rocks of this class, there is every reas...
-Texture Of An Igneous Rock
The texture of an igneous rock means the size, shape, and mode of aggregation of its constituent mineral particles. Texture is a very important means of determining the circumstances under which the r...
-Solidification
Chemical composition determines the fusibility of a rock at a given temperature. The least fusible rocks are, on the one hand, those which contain large quantities of silica, 60 to 75%, and, on the ot...
-Differentiation
Different parts of the same continuous rock-mass frequently display chemical and mineralogical variations, resulting from a process of differentiation, or segregation, of the magma. How this is brough...
-Assimilation
When we examine in the field the igneous rocks in their relations to other rock-masses, we frequently find cases where it is exceedingly difficult to account for the presence of the igneous mass, exce...
-Classification
What was said above with regard to the difficulty of classifying rocks, applies more especially to the igneous group, because of the way in which the various kinds shade into one another, since even t...
-I. The Granite Family
The molten magma, which on solidification gives rise to the rocks of this group, is very rich in silica (65 to 80%) and has from 10 to 15% of alumina; the quantity of alkalies (Na and K) is relatively...
-Granite
The granites are thoroughly crystalline rocks, of typically granitoid texture, to which they have given the name, and without any ground mass. The grains have not their proper crystalline shape, the s...
-II. The Syenite Family
In this family the magma much resembles that of the granite group, except that the quantity of silica is less (50 to 65 %); hence it is nearly or quite taken up in the formation of silicates, leaving ...
-III. The Diortte Family
The magma of these rocks has about the same silica percentages (50 to 65 %) as have the syenites, but the quantity of alkalies is less, while that of the lime and magnesia is greater. Hence orthoclase...
-IV. The Gabbro Family
In the magmas of this series the percentage of silica is much less than in the preceding groups (40 to 55%), and the quantity of alkalies is small, while that of iron, magnesia and lime is much greate...
-V. Peridotite Family
These rocks have no felspars, and in most of them the quantity of silica is below 45 %, while that of magnesia is from 35 to 48 %; they are composed almost entirely of ferro-magnesian minerals. Lim...
-Appendix. The Pyroclastic Rocks
These rocks are formed out of the fragmental materials ejected from volcanoes. The materials are of course igneous, but the rocks themselves differ from the typical igneous rocks in several important ...
-Chapter XI. The Sedimentary Rocks
The materials of which the sedimentary rocks are composed were, in the first instance at least, derived from the chemical decay or mechanical abrasion of the igneous rocks, and hence they are often ca...
-I. Aqueous Rocks
The rocks laid down under water form the larger and more important part of the sedimentary series. I. Mechanical Deposits These have resulted from the accumulation of debris derived from the des...
-A. Siliceous Rocks
In these rocks the principal component is quartz in fragments of greater or less size, either angular, or more or less rounded by wear. Of the common rock-forming minerals quartz is the hardest and th...
-B. Argillaceous Rocks. Clay - Mud
Clay consists of kaolinite nearly always with large admixtures of other substances, such as exceedingly fine grains of x quartz, felspathic mud, and the like. When moist, clay is plastic, differing in...
-2. Rocks Formed by Chemical Precipitates
Rocks which have been principally or entirely formed by chemical processes are, for the most part, of locally restricted extent, and are not at all comparable to the great masses of mechanical and org...
-3. Organic Accumulations
The organically formed rocks are those whose materials were accumulated by living beings, on the death of which more or less of their substance was preserved, added to by successive generations, and f...
-Organic Accumulations. Continued
B. Siliceous Accumulations The siliceous deposits of organic origin are very much less common and less extensively developed than the calcareous, because of the relatively small amount of silica wh...
-The Hydrocarbons
The great economic importance of these substances requires that brief mention of them be made, though they can hardly be considered abundant as rocks. The natural hydrocarbons of the earth's crust bel...
-II. Aeolian Rocks
The rocks formed on dry land form less of the earth's crust than do the aqueous rocks, but they have a special importance because of the hints which they often give as to the physical geography of the...
-Chapter XII. The Structure Of Rock Masses - Stratified Rocks
In the preceding chapter we have studied the rocks which make up the crust of the earth, so far as that is accessible to observation. It remains for us to inquire how these rocks are arranged on a lar...
-Concretions, Or Nodules
Concretions, Or Nodules, are developed after the formation of strata. They are balls or irregular lumps of a material differing from that of the stratum in which they occur. They are not pebbles, whic...
-Displacements Of Stratified Rocks
It is evident that the stratified rocks which form the land must have been changed, at least relatively, from the position which they originally occupied, since the great bulk of them were laid down u...
-Strike
The line of intersection formed by the dipping bed with the plane of the horizon is called the line of strike and is necessarily at right angles to the line of dip. (See Fig. 154.) If a piece of slate...
-Folds
Folds present themselves to observation under many different aspects, all of which may be regarded as modifications of three principal types. Fig. 153. - Symmetrical folds; anticline on left, a...
-Anticlinorium And Synclinorium
The system of roughly parallel folds which are grouped together may be, when regarded as a whole, either anticlinal, rising up into a great compound arch, or synclinal, depressed into a great compound...
-Geanticline And Geosyncline
The folds and flexures which we have so far examined are those which affect the strata at the surface or at comparatively moderate depths. It is quite impossible that the whole crust can be involved i...
-Upright Or Symmetrical
In this case the two limbs of the fold dip at the same angle in opposite directions, the plane of the axis of the flexure is vertical and bisects the fold into equal halves. In asymmetrical, or inclin...
-(3) The Monoclinal Fold
The Monoclinal Fold is a somewhat exceptional type, which can hardly be regarded as a modified form of the anticline. A monoclinal flexure is a single, sharp bend connecting strata which lie at differ...
-Chapter XIII. Fractures And Dislocations Of Rocks
The rocks are often unable to accommodate themselves by bending or plastic flow to the stresses to which they are subjected, and therefore break, usually with more or less dislocation. A simple fractu...
-Fractures And Dislocations Of Rocks. Continued
It is customary in geological literature to apply the term fault to any dislocation of the rocks, in which the broken ends of the beds are carried past one another, yet, used in this manner, it includ...
-I. Radial Faults
Radial Faults are those in which the principal component of the movement has been upward, downward, or both, though subordinate movements of tilting and rotation frequently occur. However, it is not a...
-1. Normal Faults
Normal Faults (also called gravity faults) are those in which the fault-plane inclines or hades toward the downthrow side, which forms the hanging wall. It seems best to use the term normal to cover ...
-A. Strike-Faults
Strike-Faults are those which run parallel, or nearly so, to the strike of the beds. To this group belong the great normal faults, great both as to length and throw, though they may be extremely minut...
-B. Dip-Faults
These are, in general, parallel to the dip of the beds and therefore cross or branch out from the strike-faults of the same region, more or less at right angles; they are less important than strike-fa...
-II. Horizontal Faults (Or Heave-Faults)
In displacements of this class the principal direction of movement is horizontal, and in horizontal strata may readily escape detection. When the strata are inclined, a horizontal displacement produce...
-III. Pivotal Faults
In faults of the preceding groups there and these are the pivotal faults. The result of the movement is that the hanging wall drops on one side of the axis of rotation, producing a fault of the normal...
-Thrusts
A thrust is like a reversed fault in that it is the result of compression and that the inclination or hade of the fault is toward the upthrow side, which is the hanging wall, but differs in the tenden...
-II. Fold-Thrusts
Fold-Thrusts are intimately connected with folds and occur only among folded sedimentary rocks; they may arise by plication and inversion, usually between an overturned anticline and the adjoining syn...
-III. Surface-Thrusts
Surface-Thrusts, as their name implies, are formed at the earth's surface, where a rigid, gently inclined stratum that crops out of the ground is subjected to lateral compression and thrust forward ov...
-The Causes Of Folding And Dislocation
Like all processes which take place deep within the interior of the earth, the causes of crustal deformations are very obscure and there is much difference of opinion concerning them. The view which i...
-The Causes Of Folding And Dislocation. Continued
A factor of much importance in determining the character and position of folds is the mode in which the strata were originally laid down. As we have already learned, the sheets of sediment which cover...
-Chapter XIV. Joints. - Structures Due To Erosion
With the exception of loose, incoherent masses, such as soil, gravel, sand, etc., all rocks which are accessible to observation, are divided into blocks of greater or less size by systems of cracks an...
-Cause Of Joints (Rocks)
With regard to the manner of their production, joints may be classified into two series: (1) those which are due to tension, the rock usually parting in planes normal to the directions of tension; (2)...
-Structures Due To Erosion. Unconformity
We have hitherto considered the stratified rocks as made up of beds which follow upon one another, in orderly sequence, and as being affected alike by the elevation or depression, folding or dislocati...
-Overlap
When a .series of strata is deposited in a basin with sloping sides, or one sloping side, each bed will extend farther than the one upon which it lies, and thus in a thick mass of strata, if the shelv...
-Contemporaneous Erosion
It was stated above that the definition of unconformity, as given, would include certain structures, which, nevertheless, must be distinguished from it: one of these is contemporaneous erosion. This s...
-Outliers
An outlier is an isolated mass of strata, which is surrounded on all sides by beds older than itself. This definition does not imply that the older beds must actually rise to the level of the outlier ...
-Chapter XV. Unstratified Or Massive Rocks
The unstratified or massive rocks have risen in a molten state from below toward the surface, though by no means always reaching it, and have forced, or perhaps have sometimes melted, their way throug...
-I. Ancient Volcanoes And Their Rocks. Volcanic Necks
Volcanoes, like all other mountains, are sub ject to the destructive effects of the atmosphere, rivers, and the sea. In an active volcano the upbuilding by lava flows and frag-mental ejections more th...
-II. Rocks Solidified Below The Surface (Plutonic)
We now come to a series of rocks which no one has ever observed in the course of formation, because they were solidified at greater or less depths underground. When such masses are exposed to view, it...
-Dykes
A dyke is a vertical or steeply inclined wall of igneous rock which was forced up into a fissure when molten and there consolidated. Dykes of a certain kind may actually be seen in the making, as when...
-Sills Or Intrusive Sheets
These are horizontal or moderately inclined masses of igneous rock, which have small thickness as compared with their lateral extent. Sheets conform to the bedding-planes of the strata, often running ...
-Laccoliths
A laccolith (or laccolite) is a large, lenticular mass of igneous rock, filling a chamber which it has made for itself by lifting the overlying strata into a dome-like shape; the magma was supplied fr...
-2. Subjacent Bodies
The mode in which the plutonic masses of this group have reached their present position is highly problematical and still forms the subject of a lively discussion, to which attention has already been ...
-The Mechanics Of Intrusion
As in all questions which deal with the subterranean agencies, the exact manner in which molten magmas make their way up 2D through the overlying rocks is veiled in obscurity; in fact, it is the unsol...
-Chapter XVI. Metamorphism And Metamorphic Rocks
By the term metamorphism is meant the profound transformation of a rock from its original condition by means other than those of disintegration. The incipient changes of the latter class may very grea...
-I. Contact Metamorphism
This is the change effected in surrounding rocks by igneous magmas. There is a difference between the effects produced by a surface lava flow and those caused by a plutonic intrusive. In the former ca...
-II. Regional Or Dynamic Metamorphism
This term applies to the reconstruction of rocks upon a great scale, in areas covering, it may be, thousands of square miles, and evidently other processes in addition to those of contact metamorphism...
-Cleavage And Fissility
Cleavage is a capacity present in some rocks to break in certain directions more easily than in others, while fissility is a structure in some rocks, by virtue of which they are already separated i...
-Cleavage And Fissility. Continued
Igneous masses, when subjected to the same processes, give rise to rocks entirely similar to those made by the metamorphism of sediments, so that it is sometimes impossible to distinguish between them...
-The Metamorphic Rocks
In the scheme of classification it is not yet practicable to separate the metamorphic rocks of igneous origin from those which are transformed sediments, for it is often impossible to distinguish one ...
-Slate And Phyllite
Slate is a fine-grained, dense, and hard rock, which, when metamorphosed by compression, is cleaved. It results from the transformation of clay shales, fine arkose, and sometimes of volcanic tuffs. Cr...
-B. Foliated Rocks
The foliated or schistose rocks are those which are divided into rudely parallel planes, with rough or undulating surfaces, due to the flakes and spangles of some mineral. The planes of foliation may ...
-Chapter XVII. Mineral Veins And Ore Deposits
Mineral veins and ore deposits are of the greatest economic importance and have therefore received a great deal of attention, and a very extensive literature has grown up concerning them. Obviously, b...
-II. Ore Deposits
The term ore implies an economic conception and means a source of supply of a metal which can be profitably worked, hence the proportion of the metallic constituent which must be present for profitabl...
-Ores Due To Magmatic Segregation
In our study of the igneous rocks, we learned that deep-seated molten masses in the slow process of cooling and consolidation frequently undergo differentiation, so that different parts of the same co...
-Ores Due To Contact Metamorphism
When the country rock, which is invaded by a plutonic mass, is of a kind that permits extensive penetration by the magmatic vapours and gases, metamorphism may result for a considerable distance from ...
-Metalliferous Veins (Or Lodes)
These are particular varieties of mineral veins, the principal characters of which have been given in the preceding section. Metalliferous veins are no exception to the rule that subterranean activiti...
-Secondary Enrichment Of Veins
The outcrop of a mineral vein is much altered by weathering; the depth to which this alteration penetrates is determined by the level of the ground water. For example, in the deeper portion of many go...
-Ore Deposits Formed By Surface Waters
The ore bodies of this class are formed by the concentration of the metals disseminated in the rocks, through solution and deposition by surface waters. Such deposits are made not far from the surface...
-Summary Of Structural Geology
Structural geology brings vividly before us the innumerable changes through which the earth's surface has passed, and which are recorded in the rocks. The sedimentary rocks, originally laid down under...
-Part III. Geo Morphology. Chapter XVIII. The Geographical Cycle
Geomorphology, or physiography, is the study of the topographical features of the earth, and of the means by which, and the manner in which, they have been produced. In this country the term physiogra...
-The Sea
The work of the sea is confined to the coast-line, which it cuts back by the impact of its waves and currents. Speaking broadly, the waves do but little effective work below the limits of low tide, an...
-The Arid Cycle
The essential features of the arid climate . . . are: so small a rainfall that plant growth is scanty, that no basins of initial deformation are filled to overflowing, that no large trunk rivers are ...
-Chapter XIX. Land Sculpture
While the final effect of the subaerial denuding agencies is to sweep away all relief, and to cut the land surface down to low-lying base-levels or peneplains, yet in the process great irregularities ...
-Forms In Inclined Strata
Inclined or tilted strata give rise to a different class of topographical forms. If, as is generally the case, harder and softer strata alternate, the latter will be swept away more rapidly than the f...
-Forms In Folded Strata
A region of folded strata is, in the first instance, thrown into a series of ridges and valleys, the ridges formed by anticlines and the valleys by synclines; in other words, the topography is tectoni...
-Forms In Volcanic Rocks
Volcanic topography is primarily constructive. The cones vary in form and height in accordance with the amount and character of the material of which they are composed, and the nature of the eruptions...
-Forms In Plutonic Rocks
It is exceptional that topographica\ features can be definitely referred to the constructive or tectonic effect of intrusive plutonic bodies, for the obvious reason that the presence of a plutonic mas...
-Chapter XX. Topography As Determined By Faults And Joints
Not uncommonly faults have no direct effect upon topography, or whatever influence they may originally have exerted has been lost, denudation having worn down the two sides to the same level or to a c...
-Topography As Determined By Faults And Joints. Continued
Along the entire eastern coast of Asia the topography is controlled by gigantic systems of faults. The zigzag mountain ranges which bound the coastal plains on the west have a general trend approximat...
-The Topographical Influence Of Joints
As we have repeatedly had occasion to observe, all firm and co herent rocks are divided by sets of joints into blocks of varying sizes and shapes, each kind of rock tending to display a certain degree...
-Chapter XXI. Adjustment Of Rivers
Rivers are among the most powerful of the agents of topographical development, and it is important to understand something of their modes of change and adjustment. These changes are sometimes exceedin...
-Consequent Rivers
A river has its stages of development, youth, maturity, and old age, just as has a land surface, each stage displaying its characteristic marks. When an entirely new land surface is upheaved from the ...
-Antecedent Rivers
Another way in which rivers have been enabled to cut their way through opposing ranges of hills and even mountains is by occupying the district before the hills or mountains were made. Such streams ar...
-Superimposed' Rivers
An old land-surface with well-defined topography may be deeply buried under newer accumulations, as of lava floods, great bodies of volcanic ash and tuff, sheets of glacial drift, lake deposits, or, a...
-Subsequent Streams
As a river system approaches maturity, and as the drainage of the area becomes more complete, it will increase the number of its branches. Those branches which were not at all represented in the youth...
-Adjustment Of Rivers
However the streams of a district may have been established in the first instance, whether they were consequent, antecedent, or superimposed, they are liable to changes more or less profound and far-r...
-Accidents To Rivers
This term is employed to express the interruptions which hinder or prevent the normal development of a river system. The diastrophic changes and their effects we have already considered, but there are...
-Chapter XXII. Sea-Coasts
The sea-coast is not merely a line, but a zone of varying breadth, sloping toward the sea, and with a subaerial and a submarine portion. The submarine portion of the coast frequently continues the slo...
-1. Regular Coasts
Regular Coasts continue for great distances without notable indentations and, for the most part, in gentle curves, convex toward the land, which are connected by curved lines or meet at obtuse angle...
-2. Irregular Coasts
Irregular Coasts display a great variety of forms due to the manner of their origin, and several subdivisions are employed to express this diversity of origin. All the forms, however, have this in com...
-A. Fjord Coasts
Fjord Coasts are found in the high latitudes of both hemispheres and in regions which have undergone intense glaciation; in the northern hemisphere they are limited by the 49th parallel, and in the so...
-B. Rias Coasts
This term is derived from northwestern Spain, where the Ria de Vigo, de la Corufia, del Ferrol, and several others, form long, fjord-like bays, though branching little, which extend far into the land....
-C. Calas Coasts
Calas Coasts are typically displayed in the Balearic Islands and are marked by numerous short, semicircular, and rather shallow bays, separated by narrow peninsulas. On the coasts of the Red Sea the b...
-3. Lobate Coasts
In the preceding classes of irregular coasts the bays are, after all, of comparatively small dimensions, and the general trend of the coast is not greatly affected by them, but there are other coasts,...
-Relations Of Sea-Coasts To Structure
As has been repeatedly mentioned in the foregoing paragraphs, the details of coastal topography often show no obvious relations to the geological structure of the rocks. On a grand scale, however, the...
-Chapter XXIII. Mountain Ranges
The term mountain is somewhat loosely employed for any lofty eminence, and the distinction between mountains and hills, as ordinarily made, is principally a question of height. Some so-called mountain...
-Origin Of Mountain Ranges
The manner in which mountain ranges have been formed must be deduced from a careful study of their structure, for no one has ever witnessed the process of that formation. Mountain building may be goin...
-Denudation Of Mountains
Mountains as we see them are never in the shape which they would present were the forces of compression and upheaval alone concerned in their formation. Every mountain range has been profoundly affect...
-Appalachian Cycles
We have seen that any region, however lofty and rugged, must eventually be worn down to base-level, provided only that the country remain stationary with reference to the sea until the process of degr...
-Accordance Of Alpine Summits
It is perhaps generally true of very high ranges that their highest peaks and ridges are arranged so as to be in accordance. If we imagine a surface which shall everywhere touch these summit-levels, i...
-Part IV. Historical Geology. Chapter XXIV. Fossils - Geological Chronology
A fossil is the impression or remains of an animal or plant preserved in the rocks. A knowledge of fossils is indispensable to the geologist because they give him the means of establishing a consec...
-I. How Fossils Were Embedded In The Rocks
The conditions of the preservation of fossils are much more favourable to some kinds of organisms than to others. It is only under the rarest circumstances that soft, gelatinous animals, which (like j...
-How Fossils Were Embedded In The Rocks. Continued
It is on the sea-bed that the conditions are most favourable to the preservation of the greatest number and variety of fossils. Among the littoral deposits ground by the ceaseless action of the surf, ...
-II. What May Be Learned From Fossils
The principal value which fossils possess for the geologist lies in the assistance which they give him in reconstructing the history of the globe. This they do in several ways. (1) In Determining G...
-What May Be Learned From Fossils. Part 2
A geological chronology is constructed by carefully determining, first of all, the order of superposition of the stratified rocks, and next by learning the fossils characteristic of each group of stra...
-What May Be Learned From Fossils. Part 3
(2) As Evidence Of Geographical Changes We have seen that from the composition and structure of the stratified rocks themselves much may be learned concerning the geographical conditions under whic...
-III. Classification Of Geological Time
The method of making the divisions and subdivisions of geological time is not yet a fixed one, and there is much difference in the usage of various writers. The names of the divisions also have been g...
-Chapter XXV. Original Condition Of The Earth - Pre-Cambrian Periods
As we trace the history of mankind back to very ancient times, we find that the records become more and more scanty and less intelligible, until history fades into myth and tradition. Of a still earli...
-The Pre-Cambrian Periods - I. Archaean
It is unfortunate that an account of historical geology should necessarily begin with the most difficult and obscure part of the whole subject, but the treatment must be in accordance with the chronol...
-The Distribution Of The Archaean Rocks
At the outset of our historical studies it is essential to understand clearly just what is meant by the term distribution of a given formation. It means: (i) that the given rock is at the surface over...
-Origin Of The Archaean Rocks
This is a problem which has given rise to a great deal of discussion, but a solution appears to be near. Independently, in many countries, observers have reached the conclusion that these rocks are di...
-II. Algonkian
This is the name proposed by the United States Geological Survey for the great series of sedimentary and metamorphic rocks which lie between the basal Archaean complex and the oldest Palaeozoic strata...
-Life In The Algonkian
In the Grand Canon and Montana determinable fossils have been found in the less changed sedimerits, but they are too few and scanty to tell us much of the life of the times. Evidences of life are not ...
-Chapter XXVI. Palaeozoic Era - Cambrian Period
The Palaeozoic is the oldest of the three main groups into which the normal fossiliferous strata are divided; it forms the first legible volume of the earth's history, and in interpreting it speculati...
-Palaeozoic Life
Palaeozoic Life possesses an individuality not less distinctly marked than that of the group of strata, which demarcates it very sharply from the life of succeeding periods, and gives a certain unity ...
-The Palaeozoic Fauna
The Palaeozoic Fauna is largely made up of marine invertebrates, in the earlier periods entirely so; i.e. so far as we have yet learned, though land life surely began before the oldest records of it y...
-The Cambrian Period
The rocks older than the coal measures were for a long time heaped indiscriminately together, under the name of Greywacke, or Transition Rocks, and were little regarded by geologists. About 1831, t...
-The Cambrian Of Other Continents
In Europe the Cambrian is very extensively developed, with remarkable differences of thickness in different regions. The maximum thickness occurs on the western side of the continent in Wales and Spai...
-Cambrian Life
The Cambrian fauna is of extraordinary interest, because it is the most ancient that we know with any fulness, though, of course, it does not represent the beginnings of life. Almost all the great typ...
-Cambrian Life. Ccelenterata
The Hydrozoa are represented by the Grapto-lites, a series of forms which are confined to the older Palaeozoic rocks. Dictyonema (I, 6) is a complex Graptolite, found abundantly in a thin band of shal...
-Cambrian Life. Arthropoda
The only known Cambrian Arthropods are the Crustacea, and of these much the most abundant group is that of the Trilobita, which are altogether confined to the Palaeozoic rocks, and are by far the most...
-Cambrian Life. Brachiopoda
These are among the most abundant of Cambrian fossils; most of them belong to the lower order of the class (Inarticulata), in which the shells are mostly horny and the two valves are not articulated t...
-Chapter XXVII. The Ordovician (Or Lower Silurian) Period. Ordovician System
Sir Roderick Murchison divided his great Silurian system primarily into two parts, Upper and Lower. This method of classification is generally followed even at the present day, although it is widely r...
-Distribution Of Ordovician Rocks. American
The passage from Cambrian to Ordovician was gradual, without any marked physical break. Only where the Upper Cambrian is sandy, as in New York, is there a decided change in the character of sedimentat...
-Distribution Of Ordovician Rocks. Foreign
In Europe the Ordovician rocks appear to have been laid down in two distinct seas separated by a ridge of land. The northern area extends from Ireland far into Russia, while the southern is represente...
-Close Of Ordovician
At the end of the period came a time of widespread disturbance, upheaval, and mountain-making, the traces of which are still plain in North America and Europe, especially along the Atlantic slope of e...
-The Life Of The Ordovician
Ordovician life displays a notable advance over that of the Cambrian, becoming not only very much more varied and luxuriant, but also of a distinctly higher grade. During the long ages of the period a...
-The Life Of The Ordovician. Continued
Ordovician Life. The Echinodermata The Echinodermata have greatly increased in importance, and all the main subdivisions of the group are represented, all of which, except the Cystoids, first appea...
-Chapter XXVIII. The Silurian (Upper Silurian) Period
The name Silurian, like Cambrian and Ordovician, refers to Wales. The term was proposed byMurchison in 1835 for a great system of strata older than the Devonian, and was taken from the Silures, anothe...
-Distribution Of The Silurian Rocks. American
The general disturbance which closed the Ordo-vician period appears to have greatly increased the extent of the continent. A relatively narrow strip of coast lands had been added to the northern pre-C...
-The Life Of The Silurian
Silurian life is the continuation and advance of the'same organic system as flourished in the Ordovician, certain groups diminishing, others expanding; and some new groups now make their first appeara...
-Silurian Life. Plants
Our knowledge concerning the land vegetation of the Silurian is not much more definite than concerning that of the Ordovician. Most of the remains referred to land plants are of disputable character; ...
-Chapter XXIX. The Devonian Period. Devonian System
The name Devonian, taken from the English county Devonshire, was proposed by Sedgwick and Murchison in 1839; it has found universal acceptance and has passed into the geological literature of all lang...
-Devonian System. Continued
A remnant of one of the old channels is marked by a coralline limestone in northern Vermont. The Onondaga limestone is largely a coral formation, and in some places the reefs are still beautifully ...
-Distribution Of The Devonian. Foreign
The European Devonian appears in three different fades; one of these is the Old Red Sandstone, which is largely of continental origin, and lies to the north The second facies is of marine, shoal-wat...
-Devonian Life
The life of the Devonian is, in its larger outlines, very like that of the Silurian, but with many significant differences, which are due, on the one hand, to the dying out of several of the older gro...
-Devonian Life. Vertebrata
One of the most characteristic features of Devonian life is the great development of the aquatic Vertebrates, which is so striking that the period is often called the Age of Fishes. So numerous and...
-Chapter XXX. The Carboniferous Period
The name Carboniferous was given in the early part of the last century, when it was supposed that every geological system was characterized by the presence of some peculiar kind of rock. We now know t...
-Distribution Of The Carboniferous Rocks. American
The Carboniferous is divisible into two sharply marked portions, the Lower, or Mississippian, and Upper, or Pennsylvanian, a distinction which is applicable in all the continents in which the strata o...
-Distribution Of The Carboniferous Rocks. American. Part 2
The Lower Carboniferous was brought to a close by a very widespread upheaval, which removed nearly the whole Interior Sea and resulted in a very general unconformity between the Mississippian and the ...
-Distribution Of The Carboniferous Rocks. American. Part 3
The workable coal-fields of North America, belonging to the Carboniferous system, are found in several distinct areas some of which were doubtless separate basins of accumulation, while others have be...
-The Carboniferous Period In North America
The Carboniferous Period In North America was, on the whole, a time of tranquillity, with oscillations of level and shifting of the boundaries of land and sea from time to time, such as have been desc...
-The Carboniferous Period In Europe
In Europe the Carboniferous system is developed in a very interesting way. In the western and central parts of the continent (and in Great Britain) the succession of strata is very similar to that of ...
-The Carboniferous Period In Africa
Carboniferous limestones are found in Morocco and the Sahara and Egypt. In the southern part of the continent no marine rocks of the period are known. In Cape Colony the Witteberg quartzites, which ov...
-Carboniferous Life
The life of this period is thoroughly Palaeozoic and continues along the lines already marked out in the Devonian, but there are some notable changes and advances which look toward the Mesozoic order ...
-Carboniferous Life. Continued
Foraminifera For the first time these animals assume considerable importance in the earth's economy. Many genera which are still living had representatives in the Carboniferous seas, but the most c...
-The Bryozoa
The Bryozoa become much more important than they had been before, and contribute materially to the formation of the limestones. A characteristic Carboniferous genus is the screw-shaped Archimedes (XI,...
-Chapter XXXI. The Permian Period
The name Permian was given by Sir Roderick Murchison in 1841 to a series of rocks which is very extensively developed in the province of Perm in Russia. In North America the Permian followed upon the ...
-Distribution Of Permian Rocks. American
Orogenic movements in the Appalachians had probably begun in the middle Carboniferous, as was seen in the folding which inaugurated the Pottsville trough, and toward the end of the Carboniferous there...
-Distribution Of Permian Rocks. Foreign
In Europe, as in North America, the Permian is developed in two very distinct facies. Southern Europe, Sicily, and the Alps have almost purely marine rocks and faunas, which resemble those of the Texa...
-Close Of The Permian
The late Palaeozoic witnessed mountain-making disturbances on an almost world-wide scale, extending from the middle Carboniferous to the middle of the Lower Permian. In central Europe and Spain vigoro...
-Permian Life
We have to note, in the first place, that the animals and plants of the Permian are transitional between those of the Palaeozoic and those of the Mesozoic eras. Here we find the last of many types whi...
-Chapter XXXII. The Mesozoic Era - Triassic Period
The Mesozoic era, so far as we can judge, seems to have been shorter than the Palaeozoic; in North America Mesozoic rocks are very much more important and widely spread in the western half of the cont...
-The Triassic Period
The Triassic period is so named from the very conspicuous threefold subdivision of this system of strata in Germany, where its rocks were first studied in detail, and where they occupy a greater area ...
-Character And Distribution Of Triassic Rocks. European
The Trias of Europe has been so thoroughly studied and throws so much light upon American problems, that it will be profitable to depart from the usual order of treatment and take up first the develop...
-Character And Distribution Of Triassic Rocks. Part 2
Asiatic The existence of the great Mediterranean Thetys in part of the Triassic period is indicated by the oceanic deposits which occur in Asia Minor, Central Asia, Baluchistan, Afghanistan, northe...
-Character And Distribution Of Triassic Rocks. Part 3
It is sufficiently evident that the rocks of the Newark series are not marine, but just how they were accumulated is a question as to which there is much disagreement. It has been usual to consider th...
-The Life Of The Triassic
Triassic life is entirely different from anything that had preceded it, though the way for the change was already preparing in the Permian. As we have seen, the Upper Permian, if classified by its pla...
-Reptilia
It is in this class that we find the most remarkable changes; and although reptiles are common in the Permian, the abundance and diversity of the Triassic reptiles are incomparably greater. Almost all...
-The Gnathodontia
The Gnathodontia, which are very near to the Permian Pro-ganosauria, are represented by Telerpeton and Hyperodapedon. Superficially like Crocodiles, but belonging to a different order, the Parasuchia,...
-Chapter XXXIII. The Jurassic Period
William Smith, the father of historical geology, was the first to work out the divisions of the Jurassic, which he did early in the last century. The terms which he employed are local English names, a...
-Distribution Of Jurassic Rocks. American
No undoubted Jurassic strata occur in the Atlantic border of the United States, though by some authorities the uppermost part of the Trias {Newark Series) is referred to this system, and by others the...
-Distribution Of Jurassic Rocks. Foreign
The greater part of South America was above the sea during the Jurassic period, as it had been in the Trias. Marine deposits of the former period are found only along the western border of the contine...
-The Lias
The Lias has a much more restricted extension than the later Jurassic stages. At the end of the Triassic had begun a transgression of the sea (the Rhaetic) which flooded many of the inland basins, and...
-Jurassic Life
The life of the Jurassic has been preserved in wonderful fulness and variety; but with comparatively few exceptions, our knowledge of it has been principally derived from Europe, where a host of emine...
-Jurassic Life. Part 2
Mollusca The Bivalves, which had already become such important elements of the Triassic fauna, greatly increase in the Jura, their shells forming great banks and strata. Many of the genera are stil...
-Vertebrata of Jurassic Period
The Fishes have advanced much beyond those of the Trias. The Sharks have attained practically their modern condition, and the broad, flattened Rays are a new type of the order. The Chimceroids were mu...
-Birds of Jurassic Period
One of the most remarkable advances which Jurassic life has to show consists in the first appearance of the birds. As yet, only a single kind of Jurassic bird has been found, and that in the Solenhofe...
-Chapter XXXIV. The Cretaceous Period
The name Cretaceous is derived from the Latin word for chalk (Creta), because in England, where the name was early used, the thick masses of chalk are the most conspicuous members of the system. Thoug...
-Distribution Of Cretaceous Rocks. American
At the opening of the Cretaceous, the Atlantic coast of North America appears to have been farther to the eastward than it is at present; but just as had happened in the Triassic period, a long, narro...
-Distribution Of Cretaceous Rocks. American. Part 2
With the beginning of the Horsetown age, however, this northern communication was interrupted doubtless by the closing of Bering Sea, and a connection was formed with the waters of southern Asia, and ...
-Distribution Of Cretaceous Rocks. American. Part 3
On the Gulf border the Upper Cretaceous beds of Alabama and Mississippi, which were laid down in the Mississippi embayment, are in 3 stages. Below are the sands and clays of the Eutaw (300 feet) which...
-Distribution Of Cretaceous Rocks. Foreign
In South America the Cretaceous history is much like that of the northern continent. The subsidence which inaugurated the Lower Cretaceous extended the sea over the northern part of South America and ...
-Cretaceous Life
The life of the Cretaceous displays so great an advance over that of the Jurassic that the change may fairly be called a revolution. Plants If the separation between the Mesozoic and Cenozoic er...
-The Dinosaurs
The Dinosaurs continue in even greater profusion than in the Jurassic; they are, of course, much commoner and better preserved in continental deposits than in marine, and hence are best known from the...
-Chapter XXXV. Cenozoic Era - Tertiary Period
The history of the Cenozoic era brings us by gradual steps to the present order of things. Of no part of geological history have such full and diversified records been preserved as of the Cenozoic, an...
-The Tertiary Period
The names Tertiary and Quaternary are remnants of an old geological nomenclature which has lost its significance, and were proposed when the whole succession of strata was believed to be divisible int...
-The Paleocene Epoch
The term Paleocene has not been used by American geological writers, who have, however, frequently employed the more noncommittal name of post-Cretaceous. It will be an advantage to follow the Europea...
-Paleocene Life
The vegetation of the Paleocene is of essentially the same kind as that of the latest Cretaceous, the difference between the two being principally a matter of species. Among the marine invertebrates, ...
-The Eocene Epoch. American
Along the Atlantic and Gulf borders the coast-line of the Eocene closely follows that of the Cretaceous, of which only a narrow strip separates the Eocene from the Triassic and crystalline rocks of th...
-The Eocene Epoch. Foreign
The Old World Eocene has a very different development from that of North America, the eastern continents not assuming their present outlines till much later. At the close of the Cretaceous period exte...
-Eocene Life
Except for the Vertebrates, Eocene life is chiefly instructive from the manner of its distribution over the globe. Invertebrates and plants are nearly the same as modern forms, the genera, for the mos...
-Animals
Foraminifera of relatively enormous size abounded, and their shells make up great rock masses. Orbitolites is a conspicuous genus along our Gulf coasts, Nummulites in the Old World. Corals are complet...
-The Oligocene Epoch. American
The marine Oligocene is better developed and better understood on the Gulf coast than elsewhere, and therefore forms the standard of comparison. It was a period of profuse invertebrate life and stead...
-The Oligocene Epoch. Foreign
During the Eocene nearly all Germany had been land, but in the Oligocene it was invaded by the sea, which broke in from the north and covered all the northern plain, extending into Belgium, and sendin...
-Oligocene Life
The marine invertebrates so resemble those of the Eocene that any general statement of the differences is difficult; these differences are, for the most part, of species only. The Uinta contains la...
-The Miocene Epoch. American
The marine Miocene rocks, which have an enormous development on the Pacific coast, are rather scantily displayed along the Atlantic and Gulf borders. The eastern coast, which had emerged during the Ol...
-The Miocene Epoch. Foreign
In the north of Europe the sea retreated from large areas; northern Germany was now dry land, with only a relatively small bay invading it, while England was entirely above water, anji has no marine M...
-Miocene Life
The life of the Miocene is in all respects a great advance upon that of the Eocene and Oligocene. The Grasses greatly multiply and take possession of the open spaces, producing a revolution in the con...
-The Pliocene Epoch. American
The Pliocene is not a conspicuous formation in this country, and only of comparatively late years has it been recognized at all on the Atlantic coast. The movements which closed the Miocene gave to th...
-The Pliocene Epoch. Foreign
In Europe the sea generally retreated at the end of the Miocene, leaving in the north only Belgium and a small part of northern France under water. In England the sea advanced upon the land; while in ...
-Pliocene Life
The life of the Pliocene is very modern in character. Little is known of the vegetation in North America, but in Europe it is marked by the continued disappearance of the characteristically tropical p...
-Chapter XXXVI. The Quaternary Period
The Quaternary is the last of the great divisions of geological time and may be said to be still in progress, for its events led by gradual steps to the present climatic and geographical order of thin...
-The Pleistocene Or Glacial Epoch
The conception of immense ice-sheets, like those of Greenland and Antarctica, covering large parts of North America and Europe at comparatively recent geological dates, is one that at first seems to b...
-Distribution Of Pleistocene Glaciers
The ice-sheets were localized, not universal, though it is probable that the entire world felt the effects of the lowered temperature. At the time of maximum extension of the ice, it covered nearly 4,...
-Glacial And Interglacial Stages
It is still a debated question, whether there was a single Glacial age, or epoch, during which the ice-sheet, though having many episodes of advance, never entirely disappeared, or whether there were ...
-Glacial And Interglacial Stages. Continued
The Sangamon interglacial deposits are of peat, old soil, etc. A fourth recrudescence of the glacier (Iowan stage) occasioned the deposit of another till-sheet, of an extent not yet determined, which ...
-The Champlain Subsidence
In the Glacial epoch a subsidence had begun which continued until it became a very marked feature of the times. The depression was greatest toward the north and especially in the valley of the St. Law...
-The Non-Glaciated Areas
In the non-glaciated parts of the continent occur stratified Pleistocene deposits, which it is very difficult to associate with the events taking place in the glaciated area, for lack of any means of ...
-Foreign Pleistocene
The Glacial epoch in Europe ran a course remarkably parallel with its history in North America. After the first Glacial and Interglacial stages (perhaps representing the sub-Aftonian and Aftonian), ca...
-Causes Of The Glacial Climates
This is but a special case of the general problem of climatic changes in the history of the earth. We now know that the Pleistocene glaciation is not what it was once supposed to be, a unique phenomen...
-Pleistocene Life
The frequent and extreme climatic changes, of which we find such abundant evidence in the Pleistocene, caused extensive migrations and dispersions of animals and plants, and the rapid 3E succession of...
-Appendix. Animal Kingdom Classification
For convenience of reference, the system of classification of the animals and plants which has been used in the book is here given in tabular form, omitting those groups which possess no importance as...
-Vegetable Kingdom Classification
Sub-Kingdom A. Cryptogams Flowerless Plants. I. THALLOPHYTA. Class 1. Algae, Seaweeds, etc. 2. Fungi, Mushrooms, etc. II. BRYOPHYTA, Mosses. III. PTERIDOPHYTA. Class 1. Filicales, Ferns. 2...









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