Paaeontology (Gr., ancient, bvra, beings, and?.6yog, discourse; i. e., the study of ancient beings), the science which treats of the evidences of organic life upon the earth during the different past geological periods of its history. These evidences consist in the remains of plants and animals imbedded or otherwise preserved in the rocky strata or upon their surfaces, and in other indications of animal existence, such as trails, footprints, burrows, and coprolitic or other organic material found in the rocks. From very remote times men had observed these objects in the rocky strata, far above the level of the ocean. Pythagoras, Plato, Aristotle, Strabo, Seneca, and Pliny allude to the existence of marine shells at a distance from the sea; and by all the ancients their occurrence was connected with changes of the earth's surface, and was considered conclusive evidence that the rocks containing them had been formerly submerged beneath the ocean. It was only in the beginning of the 16th century, when Christian nations turned their attention to geological phenomena, that fanciful opinions were promulgated, attributing these forms to "sports of nature," lusus natures, " the plastic force of nature," which effected these resemblances; or that, dating from the first creation, they were produced at the time of the formation of crystals or of the mountains themselves.

More than a century was required to disprove this dogma; and an additional period of a century and a half was consumed in exploding the hypothesis that organized bodies had all been buried in the solid strata by Noah's Hood. During this time, however, there were not wanting those who maintained more rational opinions. In the early part of the 16th century Leonardo da Vinci, having planned and superintended some canals in the north of Italy, opposed these views, asserting that the mud of rivers flowing into the sea had covered and penetrated into the interior of the shells when they were still beneath the water. Soon after this Fracastoro, on occasion of some excavations made about the city of Verona, declared his opinion that fossil shells had all belonged to living animals, which existed and multiplied in the positions where their remains are now found. In 1552 Cardan maintained that the former presence of the sea was clearly indicated by the petrified shells. In 1580 Palissy maintained the animal origin of fossil remains, and, as is said by Fontenelle, was the first who ventured to assert, in Paris, that fossil remains of testacea and fishes had once belonged to marine animals.

In 1592 Fabio Colonna combated many of the erroneous theories of his day, and was the first to point out that some fossils had be-' longed to marine and some to terrestrial testacea. About the year 1597 Caesalpinus maintained that fossil shells were those which had been left on land by the retiring waters of the sea, and had concreted into stone during the consolidation of the soil; and Majole, coinciding with these views, suggested that these shells with the materials containing them had been thrown up by volcanic action, similar to that which produced the Monte Nuovo, near Pozzuoli, in 1538. This appears to have been the first attempt to connect the occurrence of fossil shells at high elevations with volcanic agencies. These views were subsequently more fully developed by Hooke, Moro, and Hutton, the last two centuries after Majole. During these discussions in the 16th century large collections of fossil shells and other remains had been accumulated in private cabinets and public museums, notably in that of the Vatican in Rome, and that of the museo calceolario at Verona, which was perhaps the most famous of its time. Still the progress of scientific truth was slow.

The first half of the 17th century passed away without any real advance in the views of men regarding the origin of fossils. There were many writers on the subject, who put forth the most absurd and fantastic hypotheses, all more or less yielding to the established prejudices of the period regarding the age of the world and the early conditions of things. In 1669, while it was still a prevailing opinion that fossil shells and other marine objects were not of animal origin, Steno, a Dane, previously a professor of anatomy at Padua, published his remarkable work Be Soliclo intra Solidum natural iter contento. In this he compared the shells discovered in Italian strata with their living representatives, and traced the gradations from shells which had only lost their animal gluten to those in which there had been an entire substitution of mineral matter. He demonstrated that the teeth and bones of a modern shark were identical in general character with remains found in Tuscany. He also distinguished between marine and fluviatile deposits, the latter containing remains of seeds, grasses, and trunks and leaves of trees.

In 1670 Scilla, a Sicilian painter, published a treatise on the fossils of Calabria, illustrated by good engravings; but, like many eminent men of his time, he regarded all fossil shells as proofs of the Mosaic deluge. At the same period the theologians of Italy, Germany, France, and England maintained that it was an imputation upon the sacred writings to deny that fossil organic remains were proofs of the deluge. It will be seen that from the first the Italians have been preeminently investigators in geological science; and among those who in the 18th century advanced the most philosophical views regarding organic remains, and their origin and importance, may be named Vallisnieri in 1721, Spadain 1737, Moro in 1740, Generelli in 1749, and Donati in 1750. In 1754 Tormbia published a treatise on "The Natural History of Spain," in which is given an extensive list of localities of fossils in Great Britain and the continent of Europe, Siberia, China, the Molucca islands, and elsewhere. In 1758 the botanist Gesner of Zurich published a treatise "On Petrifactions, and the Changes in the Earth which they testify." In the north of Europe the names of Bromel and Linnaeus became associated with the study of fossil organic remains in the middle of the 18th century.

In 1790 William Smith, civil engineer, published a "Tabular View of British Strata," tracing the continuity of the secondary formations over extensive areas, and recognizing them by their contained fossils. The value of the subject of fossil organic remains began now to be appreciated in France; and the names of Cuvier, Brongniart, Lamarck, and De France are associated with the scientific investigations in this department of knowledge in the early part of the 19th century. The studies of Cuvier in comparative osteology of the living and fossil vertebrates, of Lamarck and others in the mollusca, of Alexandre Brongniart on fossil Crustacea, and of Adolphe Brongniart on fossil botany, accomplished much for the advancement of palaeontology, and aided greatly in giving it rank among' the natural sciences. The names of Schlotheim, Wahlenberg, and others are connected with the investigations of organic remains in the early part of the 19th century; and from that time progress in the science has been so rapid, and authors so multiplied, that even the names cannot be enumerated in a sketch like this.

Thus it is seen that only after long continued series of observations, carried on amid prejudices which blinded the judgment, men came finally to the conclusion that fossil organic bodies are representatives of the animals which inhabited the ocean bed at successive and remote intervals; and that they occur in the rocky strata precisely as they were imbedded in the mud or sand beneath the waters, or as they lived in the littoral belt along the shore line, where they were sometimes mingled with plants or animals of terrestrial origin. - It was, as we see by the history of scientific progress, a long and tedious process to prevail upon the human mind to dismiss the notion of the sudden creation of the earth and its inhabitants, and to recognize the creative. energy extending through myriads of ages; to admit the fact that the dry land on which we stand was simply formed by the successive depositions of mud, sand, and gravel made upon the bottom or borders of the ocean, and that these were marked by the remains of those animals which lived at the time, as similar forms now live, in the oceanic waters; and finally, that these layers of rock, of whatever kind, mark certain eras, and contain an indelible record, more or less complete, of the conditions then existing, and of the changes which have brought about the later and present state of things.

After much study and patient investigation the conclusion has been reached that, with very small exceptions, the dry land has resulted from the gradual uplifting of the ocean bod, carrying with it organic and inorganic material, in undisturbed or partially disturbed condition. An investigation of these materials, constituting the earth's crust, proves that organic life has been ad effective in the earth's past as in its present conditions. It is the history, influence, and relations of this ancient organic world which constitute the science of palaeontology in all its departments, and when fully understood will give us a better knowledge of the early conditions of the surface, the gradual progress through various phases, and the clear unbroken line from the earliest organisms to the advent of man upon our planet. The beginning, rise, and progress of the science of palaeontology have been coincident with those of geology, since the latter was separated from the speculations of cosmogony, and became a science of observation and of legitimate induction. As geology was long regarded as a subordinate department of mineralogy, and sometimes of physical geography, so also it is only by slow steps that palaeontology has assumed sufficient importance to be considered apart from its kindred science.

The one characteristic feature in the rapid progress of geology during the present century has been the growing recognition of the importance of organic remains, and the increased attention and study given to this department of natural history. In all investigations among the stratified unmetamor-phic rocks, this subject is of paramount importance; and even among the metamorphic rocks the aid of palaeontology is sometimes of great advantage in our determinations. Zoology and botany have also partaken of this influence. Constant discoveries have created new demands upon the knowledge and acumen of the comparative zoologist and botanist. The imperfect, fragmentary, or obscure condition of fossil remains has demanded the closest scrutiny of their external parts and of their most intimate structure; and it is to the reaction of this study of fossil organisms upon the methods of study in the living fauna and flora that we are indebted for a better knowledge of structure, and the filling up of gaps in our series; thus giving a truer arrangement and classification of existing forms by intercalating the fossil organisms in their proper relations. - The term "fossil" may be defined, according to M. Deshayes, as follows: "An organized fossil body is one which has been imbedded in the earth at an unknown epoch, which has been there preserved, or which has left there unequivocal traces of its existence." This excludes from the term the modern remains of plants and animals which have been buried and lost by the floods, land slides, or accidental causes of our times.

This definition being adopted, it is easy to fix the limits of palaeontology. In the present action of natural causes, we see analogies for the history of fossils imbedded in the strata of the globe. Streams, floods, and the action of waves bear along gravel, sand, or silt, and deposit them in quiet waters, the heavier materials first and underneath, the lighter above and more widely diffused, forming superimposed beds, all differing more or less in composition. A long continuation of this action may produce beds of great thickness, parallel in stratification, and in the course of their slow formation shells may gather and plants may grow, and gradually become buried by the new accession of drifting material. The first condition of these deposits is horizontality; subsequent disturbing forces may lift, or break, or disarrange them, and the gradual rising or sinking of certain portions of coast line or ocean bottom, as now taking place, must eventually produce such effects as here indicated. The study of the rocky strata shows that the same conditions, the same characters, the same accidents as these prevailed during their formation; and far from the necessity of supposing violent cataclysmic force, it is only necessary to admit the carrying on of the same process, the operation of the same causes, possibly at some times more intensified, through indefinitely long periods, to produce in the greater number of instances the results which we see.

The process of fossilization gradually supervening, with the induration of the entire enclosing mass of material, we have the beds of sand, clay, and calcareous mud converted into sandstone, shale, and limestone, still enclosing the same organisms as when they formed a part of the ocean bed; and it may be regarded as certain that these deposits were originally in horizontal or essentially horizontal position. Many of these fossil organisms were living in the condition, association, and arrangement in which we now find them. Others have been transported, broken, and mingled with those of the undisturbed beds. In some instances myriads of individuals of various forms have lived and died upon the sea bed, and have remained long undisturbed and not covered by sediments, since we find them sometimes supporting and enveloped by some other organism, as a coral, a bryozoan, or the roots of crinoidea. The physical nature and condition of the older met-amorphic strata, in which we have no remains of animals (either they not then existing, or having been obliterated by physical and chemical changes), prove the conditions of sea and land to have been essentially the same then as at present.

The great extent of ancient limestone formations renders it probable that the ocean of that period was inhabited, although of the inhabitants there is no trace. From the period of the Potsdam sandstone in America and the Cambrian rocks of Europe, we find the remains of numerous forms of animal and vegetable life. We see traces of the conditions under which they lived; the sands of the sea beaches, laid bare by the ebbing tide, were rippled by the wind and trailed by the animals of that primeval ocean. From that period at least, light and heat, cloud and sunshine, rain and wind refreshed and fertilized the earth, which teemed with animal and vegetable existences. The testimony of living things is found in their fossil imprints, the earliest evidences of life in the remains of plants and animals imbedded in the ancient sea bottoms or stranded upon the shores. Through unnumbered ages life has presented its varied forms without cessation from its first appearance on the globe; each successive epoch, each new physical condition, whether of ocean bed or shore, of moist or of dry land, presenting its new and peculiar fauna or flora.

In the course of these incalculable periods the aspect and character of the existences have changed, and there has been, if not a regular progression, yet in the main a wonderful advance over the earlier organisms. The relations of these fossiliferous beds one to another have led to the recognition of geological periods; and these periods are verified over wide areas of country, continuously or interruptedly, even to the extent of the two hemispheres. It is from the occurrence of certain peculiar forms, or an assemblage of them, in these strata, that the period or geological age can be determined. - A remarkable feature which strikes the observer is the great number of types that have appeared in a limited geological period. Trilobites, for example, lived in epochs of limited range; also the great reptiles, the pterodactyls, and certain forms of fishes, as well as some of the lower orgau-isms. Many of these are so peculiar that their appearance or disappearance is at once noticed. They are wanting in the most ancient epochs; afterward they are developed in abundance, and more or less gradually disappear, leaving no trace in subsequent periods. This is equally true of all the other forms; and scarcely any extend over more than a small number of geological periods.

In the most ancient epochs the greater number of forms have not existed; there we would search in vain for fishes, reptiles, birds, and mammifers. All our fossil fishes belong to geological formations relatively recent. In the mollusks, the articulates, and the radiates, the greater number of species appear after the ancient epochs, and successively in each of the subsequent ones; while a few types, beginning in the earlier geological periods, have been continued to the recent, or. even to present times. This is notably true of the linguloid type, although not of the true lingnla. Other species have had a brief existence. Created early, they disappear before the recent epochs, and in the fact of their early appearance, as a rule, is the certainty of their prompt disappearance. Some forms which lived in the intermediate epochs are completely ■wanting in the older and in the newer formations. In regard to the number of fossil genera which have had a limited duration, M. d'Orbi-gny enumerated, from about 1,600 then known, only about 16 which occur in all the periods; and while the whole number of genera has been since that time greatly augmented by new discoveries, a critical study will probably prove that fewer than 16 are common throughout the whole.

It sometimes happens that one or more species may appear at an earlier epoch, rare or common, but usually restricted to a limited area, and, having disappeared for an interval of one or two epochs, may reappear in greater numbers and over a far wider extent, and in association with an entirely different fauna from the first; but such cases are exceptions. M. Barrande has designated species in this mode of occurrence as colonies, and has shown that colonies are of common occurrence in the palaeozoic rocks of Bohemia. As a rule, the extinction of a fauna at the close of any geological epoch depends upon the degree of change in the sediments. Where the change is abrupt, the fauna is more likely to be entirely cut off; while if the change be in less degree, some of the species may survive. Again, where the fauna is apparently destroyed, from a change in the character of the sediments, continued perhaps for a considerable time, yet on a recurrence of the former physical conditions some of the species of the preceding epoch do reappear.

So dependent upon and connected with the surrounding physical influences is the fauna, that sometimes, after a considerable interval of change, and the existence of an entirely different fauna, a recurrence Of former conditions, though not bringing back the same species, will bring a group of similar forms and of the same genera, and sometimes species scarcely distinguishable from those of the preexisting fauna. - Since all observation has proved that no species continues through all the geological eras, and few if any are found in more than two periods, we are warranted in inferring a law of limited duration in time for each species. The effects of this law may appear, in the general results, in two ways: either that each species is altogether independent of others in its appearance and disappearance, or that those species appearing together for the first time have also disappeared together. In the first case there would be a continued series of modifications in animal populations, and consequently an impossibility of finding in the zoological characters any defined limits for geological periods. In the second case there would be strong lines of demarcation between the disappearance of species and the appearance of those which replace them.

In order to decide among the geological faunas whether the rule is the independence of the species or the combination of the above two conditions, and taking into consideration only those faunas living in the same or proximate localities, it would be inferred that the phenomena which can produce a renewal of the zoological population must extend their action to almost the totality of species. The principal proofs of this conclusion are to be found in the observation of geological facts. Individual species nevertheless do die out without geological changes, but of themselves in the midst of conditions in which they lived and flourished. If in fossil-iferous deposits we observe the line of contact of beds, it will be found that the fossil forms are nearly always very restricted. Sometimes a formation characterized by its fossils succeeds without gradation to another not less distinct in its fossil characters. Sometimes a non-fossiliferous bed occurs between two fos-siliferpus formations; but rarely do we find a deposit containing in their normal condition the fossils of the bed below it, mingled with those of the bed by which it is succeeded.

We shall usually find that where there is a mingling of the species of two formations, this single member containing them is the representative of two distinct beds in some other part of the geological field, and combines in some degree the physical characters of both. In some cases this fact may perhaps be explained by admitting that the cause of extinction has operated generally upon the fauna, but that this action has been locally circumscribed, while the two faunas continued their existence in distant localities, beyond the reach of this influence. The question of the duration of species has divided naturalists into two parties. Those who maintain their limited duration hold that the extinction of all contemporaneous faunas took place simultaneously over the whole extent of their geographical distribution; that the species of each geological period have lived only in that period; and that no one species can be found in formations of different ages. They hold that species so occurring which have been considered identical must be in reality distinct. The solution of this question is of very great palae-ontological interest. If fossils are special to the formations, they characterize them with a complete certainty.

If some are special and some are common to several formations, a part only can furnish conclusions, and hence a source of uncertainty and chances of error. The united experience of observers goes to prove that some species are restricted to certain formations, and are therefore characteristic of those formations, while others have a wider geological range, and cannot be wholly relied on for the determination of age among the strata; and in the study of a group of fossils, no careful naturalist will do otherwise than base his conclusions accordingly. It is nevertheless true that sometimes, from erroneous determinations, the same fossil species have been catalogued as from different formations; and there has also been a want of unity of opinion among geologists in regard to the limits of formations, while in disturbed regions it may not have been possible to define the limits, and thus the collections show an admixture of fossils which are elsewhere known to belong to different formations. Established facts in palaeontology prove that the limited duration of species is the general rule; but at the same time the rule has exceptions. 1. Some species, being more robust, more prolific, or living under more favorable circumstances, may have resisted causes of destruction which prevailed over their associates. 2. The causes of extinction have rarely operated uniformly or with the same force over the entire geographical extent of the fauna of any period.

Examples might be cited where the coming in of 1,000 or 2,000 ft. of sediment destroyed the previous fauna over many hundreds of miles in extent; and yet beyond the thinning margin of this deposit remains of the preceding fauna are found in contact with the overlying formation, and the fossils of the two eras are mingled, although apparently not having lived at the same time. We infer, therefore, that upon the extreme limits of the disturbed areas there may have been basins where some of the animals escaped, and thus afterward mingled with the new population. In general such basins, being beyond the geological movement, are marked by the small accumulation of sediments and thinner beds. M. d'Archiac and M. de Ver-neuil have observed that the persistence of species is connected or corresponds with the extent of their geographical distribution. " The species which are found at the same time in many points and in far separated countries are almost always those which have lived during the formation of several successive epochs." ("Transactions of the Geological Society," 2d series, vol. vi., p. 335.) This may be regarded as true in general, and for the same reason they may have continued their existence; but we have an exception worthy of note in the brachiopodous genus tropidoleptw, which first appears in the Hamilton group, and occurs in this group from near the Hudson to beyond the Mississippi, and is found likewise in Europe, while neither the genus nor any form of the type is known in any later formation.

With a few individual exceptions, the differences which exist between the lost or fossil faunas and the existing animals are the greater according as the former are more ancient. The recent forms are more varied; the diversity of animal organization has augmented in the lapse of time. But this does not warrant the inference that because the most ancient faunas are composed of animals of lower organization, the degree of perfection, as a rule, increases as we approach the more recent epochs. We find the more and the less perfect, or the lower and the more highly organized, living contemporaneously in the later geological periods, and each epoch presenting a fauna and a flora adapted to the existing physical conditions. The order of appearance of different types has been shown to represent the phases of embryonic development. The comparison of faunas of different epochs shows that the temperature has varied upon the surface of the globe, and that the areas of varying temperature have not. corresponded with the present, but have resulted from physical causes existing at the time, producing wider areas of uniform conditions; and to this cause may be attributed the fact that the species of the ancient formations have had a wider geographical distribution than those of the present time.

In conclusion we find that fossil animals were constructed upon the same plan as the existing animals; and that the same zoological principles are applicable in their study and classification.