Atlantic Ocean, that branch of the general ocean which separates the continents of Europe and Africa from America. Its oldest name among the ancients was simply the Ocean ( ); it was afterward named the Atlantic ocean from Mount Atlas, which rises near its shores. It was known and navigated by the Phoenicians long before the beginning of Greek historical records. Some of their colonies on its coasts are said to have been founded as early as 1100 B. C, and their commerce extended to the British islands and the Baltic. To the south they went equally far, and are believed to have even circumnavigated Africa six centuries before Christ, about the same time that the more timid Greeks recorded the passage of the first navigator of their nation through the strait of Gibraltar. But the real importance of this ocean as the great highway of modern civilization dates from the 14th and 15th centuries, when the outlying groups of islands, the Canaries, Madeira, and the Azores, were first visited, and finally Columbus, cutting loose from coasting voyages, struck across its unknown waste to the discovery of a new world.
I. Geographical Description. The limits of the Atlantic ocean have been taken rather arbitrarily, generally between the Arctic circle and a line drawn from Cape Horn to the Cape of Good Hope. In physical geography it is a branch of the great southern ocean, forming a deep gulf of which the Arctic ocean is the blind end. Taken as a whole, the Atlantic has the shape of an irregular broad canal running north and south, with a deep bend to the west in the middle of its course. The projecting angles of the bordering continents are said by Humboldt to correspond to the reentering ones on the opposite side. But in reality this correspondence is somewhat distorted, and thus narrows are formed by which the Atlantic is divided into three principal basins: the southern or Ethiopic, from the Antarctic ocean to the narrows between Cape San Roque and Senegambia; the middle or Atlantic proper, from the same narrows to the range of islands formed by the British and Faroe islands and Iceland; and the northern or Arctic. The Atlantic proper contrasts strongly with the Ethiopic by the great development of its shore line and the number of lateral arms or mediterranean seas in communication with it.
Such are the Caribbean sea, the gulfs of Mexico and of St. Lawrence, Baffin and Hudson bays, the Baltic, the North sea or German ocean, the Irish sea, and the Mediterranean with its dependencies the Adriatic and the Black sea. In the Ethiopic ocean, on the contrary, the coasts are very uniform, with few indentations or bays, and no inland seas at all. The watershed of the continents bordering on the Atlantic basin is of remarkable extent, all the other oceans of the earth put together receiving but a fraction of the fresh-water drainage in comparison. Several rivers of Asia and one or two in northwestern America can alone bear a comparison with those of the Atlantic basin. The number of islands in the Atlantic ocean is small when compared with those of the Pacific. Leaving aside those islands which are merely detached parts of the continents, we can count scarcely more than a dozen groups. Like most of that class, they are principally of volcanic origin. Of coral islands, so numerous in the Pacific, there are but two groups, the Bermudas and the Bahamas. II. Depth, and Figure of the Bottom. The means employed for ascertaining the depth are generally modifications of the old-fashioned lead and line. In moderate depths this method suffices in its simplest form.
In great depths, however, its indications are apt to be untrustworthy, because the shock of the lead on the bottom ceases to be felt, and the line continues to run by its own weight or is carried off by currents without sensibly slackening. Sounding with a small line or twine, to be abandoned together with the weight at each cast, was tried, but failed for want of means to determine when the bottom was reached. No sounding being now considered trustworthy unless a specimen of bottom is brought up as a proof that the lead has touched, it was found desirable to be relieved of the labor of hauling up the weight, and to bring up only the small apparatus and to collect the mud or sand. This was first accomplished by Lieut. Brooke's apparatus, a perforated cannon ball suspended in a sling which unhooks itself when the tension is relieved; an iron rod passing through the hole in the ball is provided with a contrivance to bring up a specimen, and is the only weight remaining on the line. Lieut, (now Admiral) Sands substituted two hemispheres for the solid shot, falling off on each side of the central rod, thus allowing a larger specimen cup to be employed.
An original method proposed by Prof. Trowbridge consists in paying out the line (a small but strong twine) from a coil carried down with the weight, thus avoiding the friction of the line in passing through the water. The depth is registered by a screw similar to Mas-sey's. Propositions for sounding without line have been numerous, the weight carrying down a float which is released on the bottom and returns to the surface; but none have been successful. In the United States coast survey deep-sea soundings are now usually made with a strong line and a heavy weight; detaching the latter is not considered of great importance, since the hauling up is done by steam. The depth is registered by Massey's indicator, based on the principle of a propeller screw, free to revolve in passing downward, and communicating its motion to a set of wheels registering the number of revolutions. It is clamped loosely to a spindle so as to be free from the torsion of the line, and is carefully tested and its error determined in moderate depths. The Atlantic ocean in its northern basin is better known with regard to depth than any of the others; nevertheless, there is need of more soundings before we can form a true idea of the figure of its bottom.
Most of our knowledge of it has been acquired during the last 30 years. Before that, a few soundings, now mostly considered untrustworthy, and some theoretical speculations, were the sum of our knowledge. Dr. Young deduced, chiefly from the theory of tides, a depth of about 15,000 ft. for the Atlantic, which is probably not far from the truth. Laplace supposed the mean depth of the ocean to be of the same order as the mean elevation of the land. But his supposed mean height of the land, 3,000 ft. (Humboldt estimated it more correctly at 1,000), was much too small to represent the mean depth of the ocean. Among the first connected series of deep-sea soundings were those made by the United States coast survey in connection with the exploration of the Gulf stream, those of Capt. Lee and Capt. Berryman in the brig Dolphin, of Sir Leopold McClintock in the Bulldog, and others. When the projects for laying submarine telegraph cables across the ocean began to assume importance, a sudden impetus was given to deep-sea sounding; complete sections across the ocean were explored in different directions, and the whole subject appeared much less formidable than before.
After such feats as finding and grappling successfully a broken cable in mid-ocean and in nearly two thousand fathoms, the mere fact of sounding to obtain the depth appeared very simple. In late years a new scientific interest has arisen in the study of the deep-sea bottom by means of the dredge, and numerous soundings have been taken in connection with it in Europe and America. In studying a chart of the ocean containing many soundings it will be observed that on leaving the shore, in the greater number of cases, the depth does not increase regularly or according to a uniform slope, but that the bottom forms as it were a terrace around the continents, sloping very gradually down to a certain depth, from which there is a much more rapid descent into deep water. This depth we may assume at about 100 fathoms, and that line is generally marked on the maps; but it is really somewhat less, probably in the neighborhood of 80 fathoms. We may, for instance, find that we must sail 100 m. from the shore to find 100 fathoms depth; but in 10 m. more the lead would sink to 1,000. Hence, should the level of the ocean sink 100 fathoms, a large addition of territory would be made to the continents; 100 fathoms more would increase this addition by a mere narrow strip, very steep toward the sea.
This terrace probably marks the ancient margin of the continents, and has been gradually formed by the encroachment of the ocean on the land. Hence it is as a rule wider on coasts formed of materials easily disintegrated than on those formed of hard rocks. The terrace is narrow on the coast of Spain and Portugal, and widens largely from the bay of Biscay northward, extending from 50 to 100 m. outside of the British islands, which it embraces together with the whole North sea. It is narrow along the coast of Norway, but extends from Spitzbergen half way to Cape North. On the coast of North America it is very wide, though interrupted at several points, from Newfoundland to Cape Cod, embracing all the banks. South of Cape Cod it is from 60 to 100 m. broad, narrowest at Cape Hatteras and tapering off toward Florida, but wide again on the W. side of this peninsula. The West Indies generally rise out of deep water. The terrace along the coast of South America varies generally from 60 to 100 m. in breadth, but becomes much wider S. of the Rio de la Plata, so as to include the Falklands. At the Cape of Good Hope it extends about 100 m.
S. It has not yet been developed by observation along the W. coast of Africa. With regard to the depth of the trough of the South Atlantic ocean, we have little information. Some of the supposed deepest soundings on record, from 7,000 to 8,000 fathoms, were made off the coast of South America, but they are entirely discredited now. From a few trustworthy ones it is fair to suppose this basin to have what is probably the average depth of all oceans, viz., from 2,000 to 3,000 fathoms. (It may be stated in passing, that for the Pacific ocean the average depth between Japan and California, deduced from the velocity of earthquake waves,. was found a little over 2,000 fathoms, between Chili and the Sandwich Islands 2,500, and between Chili and New Zealand only 1,500 fathoms.) Of the North Atlantic more is known than of any other ocean. The lines of soundings taken from England and France to Newfoundland, for the telegraph cables, show that no depth in that part exceeds 2,400 fathoms. From these and other soundings it appears that the bed of the North Atlantic consists of two valleys separated by a broad ridge running from the Azores to Iceland. The depth over the ridge is always less than 2,000 fathoms, generally about 1,500; it widens and shoals toward the north, forming there a wide plateau embracing both Iceland and the Faroe islands, with a depth of little more than 300 fathoms.
The eastern valley varies between 2,000 and 2,500 fathoms, seems to extend to the equator, and shoals and tapers toward the north, turning at the same time toward the northeast, until it is reduced to the narrow channel between the Shetland and Faroe islands, with 600 fathoms. Beyond this point it cannot be followed for want of data. The western valley is not well known in its southern and middle part. It is probably very broad in the great bay formed between the West Indies, the United States, and Newfoundland, depths of over 3,000 fathoms being reported S. of the Bermudas. Very deep water, 4,580 fathoms, is said to have been found a short distance S. of the Grand Bank of Newfoundland, but this has not yet been corroborated by additional soundings. The valley then passes E. of the banks, gradually shoaling, and, after sending an offset into Davis strait, passes into the Arctic ocean through the narrow passage between Iceland and Greenland, having there a probable depth of a little more than 1,000 fathoms. Of the seas communicating with the Atlantic, the Mediterranean in its two basins reaches a depth of about 1,600 fathoms in the western and 2,200 in the eastern; and the Black sea a depth of 800 to 900 fathoms.
The whole Mediterranean system is separated from the Atlantic by a barrier of 150 to 200 fathoms at the strait of Gibraltar. The Caribbean sea is deep, reaching to about 2,500 fathoms in some parts, and the passages between the Windward Islands are in some places more than 1,000 fathoms. The passage through the strait of Yucatan has about the same depth, and the gulf of Mexico may reach 2,000 fathoms in its central part. Its communications with the Atlantic through the strait of Florida and the Old Bahama channel do not exceed 400 or 500 fathoms. - From what we know at present of the Atlantic ocean bottom, it appears to be entirely destitute of any submarine chains of mountains analogous to those we have on land; there are no steep valleys, no bare rocks, in fact none of that variety of surface which on dry land contributes so much to the beauty of the scenery. For incalculable ages a slow but permanent shower of organic debris has been descending from the surface, which, mingling at the bottom with the skeletons of its inhabitants, has formed a uniform layer of a soft calcareous ooze of unknown thickness, covering the accidents of the bottom as a snowstorm levels the hillocks and ditches of our fields.
Being entirely unaffected by changes of temperature and of moisture, the ocean bottom cannot show the effects of weather or of erosion, the magnitude of which on the terrestrial relief is as yet greatly underrated even by many geologists. It is only in the northern parts of the ocean (and probably in the southern also) that in a certain sense the traces of atmospheric action on the surface of the bottom can be found, but only mediately. The banks of Newfoundland are, if not formed, at least increased by the sand and pebbles annually brought down, though in small quantities, from the arctic regions by the icebergs, of which this is the great melting ground. The rounded pebbles of basalt found by Wallich between the Faroe islands and Iceland, and the gravel and pebbles observed by Carpenter in the deep-sea dredgings off the Faroes, have probably also an arctic origin, drift ice having been seen, though rarely, very nearly in the same localities. The foregoing remarks apply of course only to the deep-sea basin.
On the terrace fringing the continents the force of tidal and other currents has had more effect in shaping the bottom; rocks and coral reefs lift their heads to or above the surface; in a word, there is more superficial variety, but even here it is seldom comparable to many of the subaerial reliefs. III. Constitution of the Ocean Bed. It has always been the practice in navigation to arm the sounding lead, i. e., to fill a cavity at its base with tallow (the arming). Particles of sand, stones, shells, etc, remain attached to it after a cast, and give, by their proportions, color, or size, indications of the position of a ship, frequently of great value. Hydrographers have devised more convenient means of bring-ing up specimens of the bottom. In France the sounding lance is mostly used, a pointed bar of iron projecting under the lead, and provided with notches or barbs in which the sand or mud remains. In the United States coast survey the characteristic specimens of bottom are preserved with care, in the first place as vouchers of the correctness of the data given on the charts, and secondly for purposes of scientific investigation.
Lieut. Stellwagen, U. S. N., while on coast survey duty, proposed a simple instrument for bringing up specimens, which, under the name of the Stellwagen cup, has been extensively and satisfactorily used. It consists in a conical iron cup, screwed into a rod projecting from the base of the lead, and having its opening covered by a loose leather valve. "When the lead strikes, the cup is driven into the bottom and fills, and the pressure of the water afterward keeps the cover down while hauling up. A slightly different sounding cup was invented by Admiral Sands, in which the opening into the cup is at the side and kept closed by a spring, which opens only when the cup is penetrating into the soil. In Brooke's sounding apparatus, before mentioned, the cavity at the end of the rod was at first filled with quills in which the mud lodged; later a valve was provided which was pressed over the opening by the sliding off of the cannon ball. The quantity brought up in that way was, however, always very small. The greater part of the extensive collection of specimens of soundings in the coast survey office in Washington have been procured with the Stellwagen and the Sands cups. In England the Bulldog machine, so called, has been successfully used for some years.
It is a modification of Capt. Ross's clams, and consists of a pair of scoops closing against each other and thus bringing up a considerable quantity of material. The results obtained by these different methods have been laid down in maps, in France by M. Delesse and in America by Mr. Pourtales, and thus a general idea of the geology of the bottom of the ocean has been obtained, or rather of its lithology, as M. Delesse has called it; for under water it is only the superficial layer which is brought to our knowledge; of its thickness, superposition, etc, the sounding lead can give us no idea. From these researches it appears that on the coast terrace there is, as might be expected, a great variety in the constitution of the bottom. It reflects as it were the geological formations of the adjacent shore, but with this difference, that the movement of the water produces a sifting action when agitated by the tides, winds, or currents, the heavier and harder particles remaining alone in some localities, while the lighter and finer materials are transported and deposited in others.
This accounts in part for the immense preponderance of silicious sand in the deposits of the terrace, since it is the result of the decomposition of most of the primitive rocks and of the sifting out of many of the secondary and tertiary formations. Limestones, being generally soft, are reduced to impalpable powder and form deposits of calcareous mud; while argillaceous mud results from the decomposition of clay slates, marl, and true clay beds. Large pebbles or shingle are rare at a distance from the shore, though common enough on the beaches. They seem to be covered by finer materials, except where swept by currents, as for instance in the British channel, where several banks of flints from the decomposed chalk beds are known to exist. But besides the deposits of which we have spoken, resulting from decomposition or remodelling of preexisting ones, there are real formations on a very large scale now going on. The lime dissolved in the sea water is assimilated by organized beings, animals or plants, secreted in solid form, principally as a carbonate, and, after having performed a short duty in the organic world, contributes in the form of a new inorganic body to the increase of the earth crust.
Thus we see in the vicinity of coral reefs the bottom composed of calcareous mud or sand formed by the dispersion of corals, shells, and echinoderms, and in shoaler parts largely by the decomposition of lime-secreting seaweeds. This mud or sand often consolidates into hard limestone rock, but more frequently when exposed to the atmosphere than when it remains under water. But it is chiefly in the deep-sea bed that lime deposits produced by organized beings assume gigantic proportions, at least in horizontal extent. The entire bed of the ocean as far as explored, outside of the coast terrace, is covered by a uniform layer of soft calcareous mud, called ooze by sailors, and composed chiefly of foraminifera, low organisms forming minute chambered shells, and living partly on the bottom and partly near the surface, whence they sink after death. With them are mixed the shells of floating mollusks, such as pteropods, of other mollusks inhabiting the bottom itself, the tubes of worms, the remains of bryozoa, echinoderms, corals, etc. Some silica is contributed, but in smaller proportions, by analogous process performed by sponges, poly cystinae, and diatomacem.
It is, in a word, chalk in process of formation, and has been found throughout the tropical and temperate regions; in the arctic seas observations are still wanting. Along the coast of the United States the terrace is principally sand. Mud is found in the deep gulf between Cape Cod and Cape Sable, S. of Nantucket, Martha's Vineyard, and Block island, for a distance of nearly 80 m. (Block island soundings), in the so-called mudholes off the entrance to New York harbor, and in a few other localities. A few rocky patches of small extent are found off the New England coast, near New York, and along the coast of the Carolinas. At Cape Florida the sand is replaced by the coral formation which envelops the southern extremity of the peninsula, and which may be. divided into two, the reef formation and the deep-sea coral formation; the former extends from the shores to a depth of about 90 fathoms, but receives its supplies almost solely from a region between the surface and 10 or 15 fathoms, where the reef-building corals live. The second or deep-sea coral formation extends from 90 fathoms to about 300. Beyond this depth, and sometimes even from 100 fathoms downward, the deep-sea ooze or foraminifera mud is found everywhere.
IV. Currents. Columbus, according to Dr. Kohl's "History of the Gulf Stream," was the first navigator who observed ocean currents, having noticed that in sounding in the Sargasso sea the lead appeared to be carried away from the ship, a fact which he rightly interpreted by the ship being drifted away from the lead by a surface current. In some of his later voyages he also observed the rapid flow of water through the passages among the Antilles, and the strong currents in the Caribbean sea and on the coast of Honduras. Sebastian Cabot noticed the Labrador current about the same time. The first notice of the Gulf stream, the most important of the currents of the Atlantic, is found in the journal of Alaminos, the pilot of Ponce de Leon in the expedition which led to the discovery of Florida in 1513. Alaminos, making use of his discovery, led the way in sailing down stream through the strait of Florida when carrying Cortes's despatches from Vera Cruz to Spain. In the narratives of the navigators of the 16th and 17th centuries frequent mention is made of the ocean currents, and in particular of the Gulf stream; it is therefore not a little singular that their details were so imperfectly known as late as the second half of the 18th century that they were rather an impediment than a help to navigation, at least for the intercourse between Europe and the northern parts of America. The New England whalers at that time were the best acquainted with the limits of the Gulf stream, and from one of them Benjamin Franklin obtained the information which he published in his chart of that current, intended to point out the most favorable routes between the North American colonies and the mother country.
Franklin and Blagden also pointed out the difference between the temperature of the water in the Gulf stream and outside of it. Pownall and Jonathan Williams extended our knowledge of this current; Capt. Strickland remarked its extension further N. and E. than was before suspected, and first argued the existence of the N. E. branch of the Gulf stream, about which there has been so much controversy of late. Humboldt and Scoresby also paid much attention to ocean currents, and particularly to the Gulf stream. Finally, Major Rennel undertook the discussion of all the observations of currents, and published the results of his generalizations under the title of "Investigations of the Currents of the Atlantic Ocean," a work which remains to this day the principal source of information on the subject.
The circulation of the water in the Atlantic ocean can be stated in very general terms to consist of two gigantic eddies or revolving streams, the one in the northern Atlantic, the other in the southern or Ethiopic basin; the former revolving from left to right, the other from right to left; both giving out offshoots of greater or less importance on their outer circumference. Both originate in the equatorial current, which consists of two parallel parts, the northern and southern, separated by a narrower return current, called the Guinea current. The southern equatorial current, starting from the coast of Africa and striking the coast of South America at Cape San Roque, divides itself into two branches. The southern one follows the coast of Brazil under the name of the Brazilian current, dividing about the latitude of the tropic of Capricorn into two branches, the smaller one following the coast, but gradually growing narrower and weaker, nearly as far as the extremity of South America. The larger and wider portion strikes toward the southeast in the direction of the Cape of Good Hope, under the name of the southern connecting current; a short distance west of this cape the current turns north and follows the coast of Africa, under the name of the South Atlantic current, toward the equator, where the circuit is completed.
This current is accompanied in its northern course, and between it and the coast, by a branch of the cold- Antarctic current, the waters of which can be traced for a long distance by their temperature. The northern branch of the south equatorial current follows the coast of South America from Cape San Roque to the Antilles, where it penetrates into the Caribbean sea, jointly with the larger north equatorial current. Thus a portion of the waters of the South Atlantic is carried into the North Atlantic, for which apparently no return is made as far as surface currents are concerned. After entering the Caribbean sea, the current is driven through the straits of Yucatan into the gulf of Mexico. The principal mass of the water then turns to the eastward along the northern coast of Cuba, while a smaller and less known branch is said to follow the western and northern coasts of the gulf, ultimately falling in again with the former. After passing the southern extremity of Florida the current receives the name of the Gulf stream, and passes north through the narrows of Bernini between Florida and the Bahama banks into the Atlantic ocean. It now follows the coast of the United States at a somewhat variable distance to about the latitude of Chesapeake bay, when it turns east.
On the S. side of the banks of Newfoundland it is pressed in by the polar current, and according to some authors ceases to exist as a special current. It is most probable that a portion of its waters continues its course eastward across the ocean, bending south between the Azores and the coast of Portugal, and finally returning along the coast of Africa to the equatorial current, and thus completing the circuit. A small offset enters the Mediterranean through the strait of Gibraltar. Another small branch separates at Cape Finisterre, sweeps around the bay of Biscay in a northerly direction, and dies out finally on the coast of Ireland. This is Rennel's current, named so after its discoverer. From the region east of the banks of Newfoundland, the waters of the Gulf stream or of the general ocean drift (the question being disputed) move northward toward the coasts of northern Europe, to which they carry their heat, passing the North Cape, and reaching nearly to Nova Zembla. Interweaving with the polar current, a branch passes up the N. coast of Spitzbergen, another around the west to the N. coast of Iceland, another along the W. coast of Greenland into Davis strait.
A polar current, carrying large quantities of ice at certain seasons, descends along the W. shore of Davis strait and the coasts of Labrador and Newfoundland, and passes, part of it under the Gulf stream, and part between that stream and the coast of the United States. - Cause of currents. The various theories propounded to explain the circulation of the water in the ocean have been based - 1, on the effect of permanent winds; 2, on differences of density due to evaporation; 3, on differences of density due to temperature; 4, on the rotation of the earth; 5, on difference of barometric pressure; and finally, on combinations of these causes. The first author to leave a theory of currents was Kepler, who attributed them to the rotation of the earth, remarking that as the water is only in loose contact with the earth, it cannot follow the rotation eastward as fast, and remains behind. He was followed and sustained by Varenius in I60O. Vossius and Fournier a little later adopted the heat and evaporation theories, but in a rather extravagant form, the former supposing the heat of the sun to expand and attract the water of the ocean into a kind of long mountain ridge, which, following the sun, broke on the coast of America, producing the currents running along the shore; a curious glimpse of the usual tidal theory.
Fournier supposed, on the contrary, a hollow or valley formed by evaporation in the ocean in the tropics, causing a constant rush of the polar waters to fill it up. Coming down to Franklin, we find him an advocate of the trade-wind theory for the Gulf stream, while, later, Humboldt explained the phenomenon by the rotation of the earth. Major Rennel, in his work on ocean currents, divides the currents into two classes. Drift currents, according to him, are the effect of the permanent winds on the surface of the water, by which the superficial layers are set in motion; when a drift current meets with an obstacle, the general surface is raised by accumulation, and the water in trying to return to its level produces a deeper and generally more rapid flow called a stream current. The equatorial current is an example of the former, the Gulf stream of the latter. It would take too much space to detail all the theories of modern authors, but a few must still be mentioned. Capt. M. F. Maury gave an exaggerated weight to differences of density of sea water in northern and southern parts of the ocean. Sir John Herschel, in his article on physical geography in the "Encyclopaedia Britannica," attributed the currents to the effect of the trade winds.
Before his death he seems to have fallen in with the views of Prof. Carpenter mentioned under the head of Gulf stream. Dr. Muhri of Gottingen, in his work on ocean currents, gives the following conclusions: 1. There are in ocean circulation two great movements perpendicular to each other, the one following the equator, the other the direction of the meridians. 2. The equatorial circulation results from the inertia of water with regard to the rotation of the earth; the meridional or ther-mometric circulation is caused by the difference of temperature between the polar and equatorial regions. 3. The meridional as well as the equatorial circulations exhibit two motions in contrary directions, which compensate each other and are superposed to each other in part in the thermometric circulation, on account of their unequal density. 4. The unequal distribution of the continents impedes the regularity of the great movements of circulation, and, in conjunction with the unequal relief of the bottom and the action of the winds, induces secondary currents disturbing the general motion. - Gulf stream.
The importance of this great current to the commerce and navigation of North America, to which reference has been made before, the great scientific interest it presents by its size, temperature, and influence on climate, have made it, in the words of Prof. Bache, "the great hydrographic feature of the United States coast." Under the superintendence of the late Prof. Bache, the United States coast survey has accumulated a large number of observations of that part of the stream comprised between its entrance into the straits of Florida and the region where it leaves the coast after having changed its course to the east. The observations were directed chiefly toward the determination of the depth, the figure and constitution of the bottom, and the temperature from the surface down through the whole depth. The instruments used for temperature have been of various construction. Metallic thermometers in the watch form were used, enclosed in strong brass vessels; they answered well enough, and were employed to a considerable extent in the earlier researches; but in several instances the brass box was crushed by the pressure. Self-registering thermometers in glass globes were used also, but they had the inconvenience of experiencing the changes of temperature too slowly.
Six's self-registering thermometers were used extensively, up to about 100 fathoms, beyond which they are liable to be crushed; and in all cases their indications are rendered very erroneous by the pressure. For great depths Saxton's metallic thermometer has been of great service. This instrument consists in a ribbon of two metals of different expansion, soldered together and rolled in a cylindrical spiral around a spindle, to which the movement of expansion or contraction is communicated, and by it transferred to a hand or needle moving an index over a graduated dial. The whole is enclosed in a suitable case perforated for the passage of the water. It works well, but is affected by pressure in a manner not easily explained. At present the Miller-Casella protected thermometer is used, and proves an excellent and trustworthy instrument. It is in the main a Six's self-registering maximum and minimum thermometer, the bulb of which is protected from pressure by an outer bulb blown over it and sealed round the neck, a space being left between the two bulbs, partially filled with alcohol, in order to communicate the temperature more rapidly to the inner bulb. The observations were made at a number of stations in lines or sections at right angles to the stream.
The thermometer was observed at the surface and at different depths, generally at every ten fathoms as far as 50, and at every hundred fathoms in greater depths. When the change of temperature was very rapid, the number of sections, stations, and observations was multiplied to keep pace with it. The results were arranged afterward in diagrams, where the changes of temperature were represented by curves, thus giving at a glance the distribution of heat throughout the stream. From these observations the following general deductions were made: In the sections between Florida and Cuba the highest temperatures were found near the Cuban coast, where also the greatest depth was recorded. It was observed by Mr. Mitchell that very near the coast of that island the stream had a uniform velocity and constant course for a depth of 600 fathoms, although in this depth the temperature varied 40°. The stratum of warm water was! found to be of much greater thickness or depth toward the middle of the straits than nearer shore; thus at a distance of 6 or 7 m. from Havana the layer of water above the temperature of 70° extended only to a depth of about 70 fathoms, while some 30 m. off the coast its thickness was about 180 fathoms.
The slope of the bottom is very abrupt on the Cuban coast, but much more gradual on the Florida side, where the current is also more irregular, taking sometimes even the shape of a counter current running west. It is also here affected by the winds and tides. The same character as in this section is maintained throughout the straits of Florida to the narrows of Bernini. No permanent current was found in the St. Nicholas and Santarest channels, sometimes regarded as partial feeders of the Gulf stream. Toward the narrows of Bemini the breadth and depth of the straits diminish and reach their minimum, the breadth being only 44 m. and the greatest depth 370 fathoms.
The bottom presents here some inequalities in the shape of longitudinal ridges, the effect of which is to press the cold water of the bottom toward the surface, by which the first indication is produced of those alternate bands of warmer and colder water noticed further north. The warmest water is still found nearer the eastern or right bank of the stream; but after leaving the straits, and when the stream has gradually widened, the warmest water is on the left or western edge. The stream now runs parallel to the coast, distant from it about 70 or 80 m., turning gradually to the N. E. from the due N. course it had on leaving the narrows. It approaches nearest to the land at Cape Hatteras, takes there a slightly more northern direction, and shortly after turns sharply to the east, its rather variable western edge being then about lat. 38°. The space between the shore and the stream is occupied by the cold water of the polar current, and the contrast between it and the warm water becomes more and more abrupt, particularly at some depth, so that the plane of separation received from Lieut. Bache, who first noticed it, the name of the cold wall.
At the surface the warm water overflows the cold, forming a thinned-out superficial layer, the limits of which vary somewhat according to the seasons and prevailing winds, certainly much more than the main body of the stream. The bands of cold and warm water increase in number, from three warm ones when coming out of the narrows to six or seven in the section off Sandy Hook; it must however be remarked that several of them are very vaguely defined and far from constant. In the same section the depth of the stream is still very considerable, its limits being nearly as well marked by the difference of temperature at 400 fathoms as it is nearer the surface. In the following tables the temperatures of the water at different depths are given in a form nearly as plain as in a diagram for two of the sections. The first is for the section between Cape Florida and the Bernini islands. The full line represents the surface; above it are given the distances from Cape Florida. The depths are given on the side, and are indicated across the table by dotted lines for every hundred fathoms.
The figures of the first line give the temperature from the average of the observations taken at the surface and at 5, 10, 20, and 30 fathoms; of the second line the average at 50, 70, 100, and 150 fathoms; and in the third are combined the temperatures at 200 and 300 fathoms. The figures arranged vertically over each other represent observations taken at the same station. Table II. is a similar arrangement of the observations in the section off Sandy Hook (New York). The first line gives the temperatures at the same depths as the first line of Table I.; the second line gives the averages of the observations at 40, 60, 80, and 100 fathoms; the third of the same at 200 and 300 fathoms; and the fourth the observations at 400 fathoms:
MILES FROM CAPE FLORIDA.
Steep slope to Cape Florida.
Very steep slope to Bermni.
- Greatest depth.
MILES FROM SANDY HOOK.
Both tables show the difference of temperature between the Gulf stream and the inshore cold water or polar current to be distinctly traceable down to 400 fathoms at least; indeed, in both cases the actual difference is greater near the bottom than at the surface, being in the narrows of 10° at 250 fathoms against 7° at the surface, and off Sandy Hook of about 18° at 400 fathoms, while at the surface it is only 14° or 15°. The surface differences would of course vary with the seasons, but it is proper to call attention here to the fact that the stratum of water above 60° is still nearly 300 fathoms thick in this latitude. The theory frequently propounded that the polar current underlies the Gulf stream and penetrates through the straits of Florida into the gulf of Mexico, is rendered very improbable by Mr. Mitchell's observations cited above, and by the volume of water necessarily passing through these straits to supply as large a cross section as we find off New York. It is much more probable that the cold water at the bottom of the gulf of Mexico reaches it by a much longer circuit, and perhaps a very small portion by the counter currents at Cape Florida. - The surface velocity of the Gulf stream appears to be variable, being probably affected by the wind; but although we have as yet no observations of the velocity at various depths, it is safe to assume a much greater constancy for the bulk of its waters.
According to the chart of the Atlantic ocean published by the hydrographic office in Washington, the rate of the current in the straits of Florida is from 1 to 4 m. per hour; in the narrows of Bernini, from 1 1/2 to 5 m.; off the coast of Georgia, 1 1/4 to 4 m.; off Cape Fear and Cape Hatteras, 1 1/4 to 3 3/4; off Chesapeake bay, 4 m.; and in the longitudes of Nova Scotia and Newfoundland, between 2 and 3 m. Mr. Findlay estimates it rather less: about 2 3/4 m. per hour in the narrows of Bernini, 2 1/3 off Charleston, 1 1/2 to 2 off Nantucket, and a little over 1 m. S. of the Newfoundland banks. Accurate observations at all seasons and at various depths, though difficult to make, are very much needed. - The further course of the Gulf stream after passing the banks of Newfoundland is involved in some doubt, as has been mentioned in speaking of the general system of currents of the Atlantic ocean. That water of a higher temperature than is due to the latitude reaches the northern and eastern shores of the Atlantic appears to be universally admitted.
Capt. Strickland seems to have been the first to attribute this fact to the extension of the Gulf stream, and was supported in this opinion by the authority of Humboldt and Scoresby, the latter having made a large number of observations of temperature in the Arctic ocean. Leopold von Buch, struck during his travels along the coast of Norway with the luxuriance of the vegetation in so high a latitude, the high level of the line of permanent snow, the freedom from ice of the harbor during the greater part of the winter, etc, attributed to the Gulf stream the office of bringing heat to these coasts; and his reasoning appeared to Humboldt "perfectly convincing." Gen. Sabine, during one of his voyages for pendulum experiments, made numerous observations in the Gulf stream proper, and in its supposed extension across the ocean, and along the coasts of Europe, south of England and Africa, and was convinced that both were one and the same system. Rennel was the first to shake this belief, at the time almost universal, attributing the whole easterly and northerly movement of the waters to a superficial drift produced by the prevailing S. W. winds.
It must be remarked that he ignores entirely the effect of the rotation of the earth, and of the heating and cooling of the waters at the equator and pole, joint causes which Arago was probably the first to exhibit, without, however, entering into their discussion. In very recent times the partisans of both opinions have shown a renewed activity, partly in connection with arctic, and partly with deep-sea explorations. It was in reference to the former that Dr. Petermann gave his opinion as follows: "Instead of a weak and insignificant drift from Newfoundland toward Europe, as heretofore represented, I consider the northern part of the Gulf stream one of the mightiest currents of the world, although comparatively slow, not very perceptible on the surface of the ocean, and therefore of no great moment to navigation. I do so because ocean currents have to perform other functions than merely those of a strong surface stream. In that view I conceive the Gulf stream to be a deep, permanently warm current from Newfoundland to the coasts of France, Great Britain, Scandinavia, and Iceland, up to Bear island, Jan Mayen, and Spitzbergen; and along the western coast of the latter up to the 80th degree of north latitude, thence to Nova Zembla into the polar sea, passing the northernmost capes of Siberia and the New Siberian islands, where it appears on the charts as the Polynia of the Russians, ... its influence being felt perceptibly even as far east as Cape Yakan." Numerous opponents have risen against these assertions, among them Mr. Findlay, who contends that the Gulf stream proper has not sufficient width and depth to reach the coast of Europe; that at its slow rate of progress it must lose all its heat during the passage; that after reaching Newfoundland it is totally annihilated by the Polar stream, and cannot be perceived beyond; that the Gulf stream has nothing to do with the climate of northwestern Europe, which is affected only by the general drift of the North Atlantic ocean.
To this Dr. Petermann replies that the Gulf stream is no doubt reinforced by a drift corresponding to it in direction, in the same way that a river is swelled by tributaries, without for all that losing its individuality and its name. Prof. Carpenter, in discussing the results of his deep-sea temperature observations, doubts if the Gulf stream sends any but a very small and superficial contribution to the northern seas, and is supported by the companion of his researches, Mr. Jeffreys, on zoological grounds, the latter rather premature, since we are still at the dawn of our knowledge of the deep-sea fauna. Dr. Petermann now took a very important step in the question; the differences of opinion resting chiefly on belief and theory, he undertook to collect all the observations of temperature of the water in the North Atlantic and construct charts of isotherms for every month in the year. The large amount of materials buried in Maury's wind and current charts were made available by much labor; the observations published by the Dutch government and by the Scottish and Norwegian meteorological societies, the records of sea temperatures of some of the transatlantic steamship lines, those of the Danish ships sailing to Iceland and Greenland, collected by Admiral Irminger, and those of various arctic expeditions, furnished a considerable array of data.
Of the twelve monthly charts contemplated, two only have been published, th6se for January and July. The chart for July exhibits the core of the Gulf stream at a temperature of 81.5° extending northward as high as lat. 38°, and with a temperature but slightly decreased as high as lat. 40°, and as far east as Ion. 43°. That it is not a mere drift is shown by the lower temperatures south of this tongue, which in January is shortened as might be expected. At Newfoundland the curves show the inroad made by the polar current, but in a less marked manner in winter than in summer. In July the polar current brings water at a temperature of 45.5° down to lat. 50°, while further east the Gulf stream water has still 65° in the same latitude. To the east of Newfoundland the isotherms set toward the north with two bends more marked in summer than in winter. In July the isotherm of 54.5° advances toward Iceland and the Faroe islands to lat. 61°. The warmer water follows not only the W. coast of Iceland, but passes round to the N. side of it, while on the E. and S. coast the polar current preponderates, producing a temperature lower by 5° or 6°. Between Iceland and the Faroe islands warm and cold bands of water alternate, the result of the struggle between the Gulf and polar streams, the latter carrving drift ice much further south in this region than anywhere else east of Iceland, and reducing the temperature of the water at the Faroe islands to a lower point than it has on the W. coast of Iceland, where the winter climate is not as severe as it is in many parts of New England. The isotherm of 36°, which touches Iceland in winter, extends at the same season beyond North cape; the sea at Fruholm, North cape, is in January still at a mean temperature of 37'9°. Observations are wanting to show the further extension of the Gulf stream toward the northeast.
It is met by a polar current running in the opposite direction, and cut by it into two branches, of which one runs along the W. side of Spitzbergen, the other eastward of Bear island. The further progress of this branch, which is the main one, is not known. The branch of the polar stream separating the two arms sets toward the coast of Greenland, where it is said to form a bight in the drift and field ice, reaching nearly to the coast. - In high latitudes deep-sea temperatures show in many localities an anomaly in this, that the coldest are observed near the surface, and that there is an increase of temperature with depth. Observations in the Antarctic ocean have shown the same phenomenon. It is frequently explained by comparison with the same phenomenon in fresh water, the maximum density of which is 7'2° higher than the freezing point. Although with regard to salt water the question appears still unsettled, the weight of evidence seems to point to an increase of density in the latter down to the freezing point.
In that case the colder surface temperature might be attributed to the stratum of water from melting ice, floating over warmer layers because of less density. - Some light has been afforded as to the course and origin of the currents in the northern seas by the driftwood and other materials thrown by them on the shores. The northern coast of Spitzbergen is covered with immense accumulations of driftwood, bark, pumice stone, etc.; among them Torrel found a large bean of en-tada gigalobium, a product of tropical America found on all the shores washed by the Gulf stream, from Florida to Norway. These beans are found even in the Danish colonies on the W. coast of Greenland, where they are known under the name of vettenyrer or witches' kidneys. The seeds of mucuna vrens and mimosa scandens are generally found with the former. The driftwood was pronounced by botanists to be nearly all Siberian larch, thus proving that the sea is open in summer as far as the mouths of the great Siberian rivers, and that in the locality mentioned the waters of the Gulf stream mix with those of the polar current.
The saltness of the water in different parts of the ocean, as determined by Prof. Forchham-mer, was laid down on a chart by Dr. Petcr-mann, and found to agree remarkably well with his temperature charts, the warmer or Gulf stream water being more salt than the colder or polar stream. From all the points discussed in his paper, Dr. Petermann draws the following conclusions: 1. The Gulf stream extends along the North American coast with a temperature of 77° and upward as far as lat. 37°; a temperature in winter higher than the temperature of the air in Africa under the same latitude, and higher than the temperature of the water at any time under the equator. 2. The Gulf stream turns away from the American coast in lat. 37° to 38° toward the east beyond the banks of Newfoundland to lon. 40° W., where it still has a temperature of about 75° in July and about 66° in January. From there it proceeds to the northeast, surrounding Europe to the Arctic and the White sea with a permanent current of warm water, still having a temperature of 37.8° in a latitude in which in Asia and America the mercury remains frozen for months. 3. The velocity and strength of the stream are still imperfectly known.
Findlay estimates the time for the water to travel from Florida to Europe at one or two years; Dr. Petermann, at two months. 4. The Gulf stream must be a deep and voluminous body of water, keeping away the polar ice from the coasts of Europe. The polar current presses at three places against it, E. of Newfoundland, E. of Iceland, and at Bear island. 5. These polar currents make a much deeper impression in the Gulf stream in summer than in winter. 6. In winter the Gulf stream is cut in upon much less. The polar streams are then less powerful, the polar ice being fast in the north. This is shown by Mr. Redfield's observations on the drift ice off Newfoundland. Of 100 cases of ice seen, 87 occurred in April, May, June, and July; of the remaining 13, there were 7 in March, 3 in August, 2 in February, and 1 in January; none at all in September, October, November, and December. 7. The relations of temperature within the Gulf stream itself are about the same in winter and in summer; the fluctuations between its maximum and minimum would be only about 9°. - The thermometrical results of the deep-sea expeditions in the European seas in the steamers Lightning and Porcupine in 1868, '69, and '70, have been used by Prof. Carpenter, under whose charge the observations were made, for a theory of ocean currents based on the heating and cooling of the water at the equator and pole respectively.
The remarkable fact was brought out during the first cruise that in the channel between the Faroe islands and the N. coast of Scotland a warm area exists on the bottom in close proximity to a very cold one. The warm area, S. W. of the Faroe islands, had a temperature of 41.4° at a depth of 7G7 fathoms; the cold area, only 20 m. distant, between the Faroe and Shetland islands, only 29.7° at 640 fathoms, the surface temperature being the same. Near the Rock-all bank off the W. coast of Ireland the temperature of 41° was found to extend to 775 fathoms, with a bottom temperature of 37.4° at 1,400 fathoms, and off the bay of Biscay to 800 fathoms, with a bottom temperature at 2,435 fathoms of 36.5°. Prof. Carpenter remarked on these results that the elevation of temperature in the warm area above the isotherm of its latitude could only be attributed to a supply of water from the southwest; and that the Gulf stream, meaning the warm water coming through the narrows of Florida, if it reached this locality at all, which he considers very doubtful, could only affect the most superficial stratum; and that the same could be said of the surface drift caused by southwesterly winds.
He comes to the conclusion that the presence of the body of water ranging from 100 to 600 fathoms in depth, and the range of temperature of which is from 48° to 42°, can scarcely be accounted for on any other hypothesis than that of a great general movement of equatorial water toward the polar area, of which the Gulf stream constitutes a peculiar case modified by local conditions. The arctic stream in the cold area is also a peculiar case of the general movement of the polar water toward the equator; for it is forced to pass through this, the deepest channel between Iceland and Europe, and pressed toward its S. E. shore on account of the channel's oblique position with regard to the N. and S. flow of the water. Prof. Carpenter is inclined to think that the Arctic ocean is insufficient to supply cold water enough for so great a reduction of temperature as is found in the body of water below 1,000 fathoms in the Atlantic basin, and thinks that antarctic water may also flow in past the equator as far as the tropic of Cancer; a question rather difficult to settle in the present state of our knowledge, since all we know is that under the equator bottom temperatures have been observed of 35.2° at 1,806 fathoms, and 33.6° at 2,306 fathoms.
The best evidence adduced by Prof. Carpenter for the flow of polar water on the bottom toward lower latitudes is based on his deep-sea temperatures of the Mediterranean. This closed body of water communicates with the Atlantic through the strait of Gibraltar alone, and that is too shallow to allow of a communication between the deep waters of the two basins. The Mediterranean goes down in some parts to 2,000 fathoms. The surface is hot in summer, as high as 78° sometimes, but the hot layer is shallow, 10° or 15° being lost in the first 30 fathoms. At 100 fathoms the temperature is generally 54° or 55°; beyond that depth no further reduction was observed; "whatever the temperature was at 100 fathoms, that it was at the bottom;" and this temperature is found to be the permanent temperature of the surface of the earth in that latitude. The same observer concludes that the ocean is subjected to two different circulations: a horizontal one produced by the action of the wind, the Gulf stream being an example of it; and a vertical circulation dependent on opposition of temperature.
V. Life in the Atlantic Ocean. - 1. Vegetation. The flora of the ocean, or nereis, as it has been called, is confined to a narrow belt along the shores and to the surface layer of water in mid-ocean, a strong light being necessary to its existence. With the exception of a few species of the family of zoste-racece (eelgrass, turtlegrass, grasswrack), the whole submarine vegetation belongs to the algas, plants of low organization. The limits of depth to which certain families, genera, or species are confined, are much more definite than they are for animals; they have been called zones by Edward Forbes, characterized by the prevailing types growing in each. Commencing at the surface, he called littoral zone the region between high and low water, which on rocky shores is characterized by a luxuriant growth of fucaceae principally, of which different species form further subdivisions of the zone, according to their preferences for a longer or shorter exposure to the air. Below low-water mark the laminarian zone begins, and extends to 4 or 5 fathoms; in it are found in abundance the chondrus crispvs or carrageen, the thong weed (himanthalia), and the tangle or devil's apron (laminaria). In the lower part of this zone are found the red and purple seaweeds, many of them of great delicacy and beauty.
The next zone is that of the corallines, so named from a family of seaweeds having their tissues filled with lime and simulating small corals. As a general rule seaweeds do not grow much deeper than 8 or 10 fathoms, though there are exceptions; thus the gigantic macrocystis pyrifera, found growing in 40 fathoms, and rising to the surface at an angle of 45°, and streaming on it for a distance of several ships' lengths, has been estimated to have a total growth of 700 feet. Low forms of corallines have been found at more than 200 fathoms, and diatomaceae at all explored depths. The geographical distribution of seaweeds depends much on temperature and currents. The laminarim, for instance, prefer cold water, the sargasso, the warmest. The largest forms are found in colder water, as the laminariae in the north, the macrocystis, Lessonia, Durvillea, etc, in the south. As examples of the influence of currents on the distribution, we may take padina pavonia, a West Indian species, not found in America N. of the Florida keys, but carried to the S. shore of England probably by the Gulf stream.
The macrocystis and other large antarctic seaweeds luxuriate about Tierra del Fuego and the Falkland islands; they are carried far toward the equator by the Peruvian current on the W. coast of South America, while they are kept back on the E. coast by the southerly extension of the Brazilian current. A very remarkable feature of ocean vegetation is the Sargasso sea. This name is commonly used to designate a region of the Atlantic covered by a peculiar floating seaweed, either in tangled masses of considerable extent, compared by some writers to floating prairies or submerged meadows, or simply in scattered sprigs. Columbus, as is well known, passed through these fields of seaweed in his first voyage, to the great alarm of his companions, who from previous association would naturally imagine a connection between seaweeds and rocks or shoals. Since that time, for nearlv four centuries, observation has shown that the geographical position and the abundance of these plants remain essentially unchanged.
Humboldt found that the gulf weed, as it is generally called, because found also \ in the Gulf stream, was distributed in two principal masses, the largest situated a little to the west of the meridian of Fayal and between the parallels of 25° and 36° N. Northwest winds are said to carry it sometimes to the latitudes 24° to 20°. The second or lesser bank is less known, according to the same author, and occupies a space between the Bahamas and Bermudas. Capt. Leps of the French navy has investigated the subject more recently, and places the principal bank between lon. 295 and 45° W., and lat. 21° and 33° N., with smaller scattered masses extending several degrees beyond these limits on all sides. The smaller bank he found not so well defined, the denser portion forming a band extending to the N. E. of Porto Rico and to the latitude of Bermuda. The Sargasso sea corresponds to the great centre or eddy of the North Atlantic system of currents, of which the Gulf stream forms so important a part.
The botanical name of the gulf weed is sargassum oacci-ferum (Agardh), not sargassum natans, as it is usually called in books of navigation, which is a species growing on rocks in the West Indies. It is generally found in sprigs a few inches long, with a main stem branching into secondary ones; the main stem has frequently a decaying end, while the other gives rise to fresh-growing leaves; but there is never any trace of root or place of attachment. Between the leaves, which are elongated and sharply serrate, small round air vessels, the size of currants, are supported on short peduncles. These air vessels or floats are vulgarly taken for the seeds or fruits; hence the name, derived from a Portuguese word meaning grapes, and the French names of raisins de mer and raisins du tropique (sea grapes and tropic grapes). Far from being seeds, it is a singular fact that the plant has never been observed to produce a fructification, and that it propagates only by division. Prof. Agassiz has observed that deprived of its floats the plant sinks. Humboldt, in his personal narrative, thought it might possibly grow on an undiscovered bank of 40 or 60 fathoms depth.
This opinion he afterward abandoned; but as it is still current among some persons, it may be stated here that such a bank in mid-ocean would have revealed itself by discoloration of the water before now, and to produce the immense masses of floating weed would have to be of considerable size; besides, soundings in different parts of the Sargasso sea have revealed a very great depth of the ocean in that part. It is furthermore well known that fu-coids grow only in very moderate depths, the greater number Of species being confined between tide marks. Humboldt in later works adopted the more probable supposition that the gulf weed originates and propagates where it is found. To this he was led'by the observations of Meyen, who examined several thousand specimens during a voyage across the Sargasso sea, and found them uniformly destitute of roots or fructifications. Robert Brown, however, thought the question of origin still obscure, but that the theory of propagation by ramification and division was highly probable. He thought it possible that it might have originated from some nearly allied species in the gulf of Florida, fucus natans for instance, afterward permanently modified by the circumstances in which it had been placed for ages.
Harvey, a high authority in the knowledge of seaweeds, who explored the shores of Florida and examined the fresh gulf weed, is also clearly of the opinion that it propagates only by division, whatever may have been the origin of the species. The gulf weed harbors a peculiar fauna consisting of fishes, crustacea, mollusks, and polyps. Among the fishes, a small chironectes is most abundant, which constructs a peculiar nest for its eggs, by fastening several sprigs of gulf weed together. It has been said that no similar accumulation of floating seaweed was known in any other part of the world; but a Sargasso sea, bearing the same relations to the North Pacific currents which the Atlantic one bears to the Gulf stream, is found to the northward of the Sandwich islands, and appears to occupy a still larger space. It is, however, very little known. - 2. Animals. The cold seas seem to be more favorable to the development of mammalia than the warmer ones. Thus the highest in the scale among those inhabiting the ocean, the polar bear, is found in the furthest north, and is only an occasional visitor of the shores of the Atlantic proper, when carried along by the ice.
The seal family is also most numerously represented in the arctic regions; the North Atlantic and Arctic harboring only earless seals, the South Atlantic eared seals likewise. One or two imperfectly known species are reported in the West Indies, and one in the Mediterranean. Of the manatees, which are more fresh-water than marine animals, two species are found on the American tropical shores and one in Africa. The walrus retreats from persecution further north every year, so that its original distribution is uncertain. The same may be said of some of the whales, particularly of the right whales, two species of which have been described from the north, the one confined to the frozen ocean, the other, almost extinct, inhabiting the region between this and lat. 40°. No right whales are found in the tropics, but a third species is found south of the tropic of Capricorn. The finback whales appear to frequent all the oceans except the frozen regions. The sperm whale is found chiefly in the warmer seas, S. of lat. 45° N.; it is said to pass Cape Horn, but not the Cape of Good Hope. Of the smaller cetaceans known as porpoises, the genus phocama is chiefly northern, delphinus almost universal. - Of the families of birds frequenting the Atlantic ocean, the ducks have their greatest development in the far north, visiting the temperate regions in winter; they are much more scantily represented in the South Atlantic. The auks and divers are also northern birds, and are in a great measure replaced by the penguins in the southern cold regions.
The pelican family flourishes best in the tropics, where it has its large representatives, the pelicans, frigates, phaetons, etc.; while cormorants and gannets extend as far as the cold temperate zone. The petrels, the most pelagic of birds, are seen in all latitudes, but with a strong preponderance in the southern cold region. The giant of the tribe, the albatross, visits the coast of South America as far N. as the Rio de la Plata. The gulls and terns are seen everywhere. - Of reptiles, the Atlantic has only four species of turtles, inhabiting the warmer seas, and only occasionally carried to higher latitudes by warm currents. Marine-snakes, common in the Pacific, are entirely absent in the Atlantic. - The North Atlantic is perhaps of all seas the best provided with useful fishes. The gadoids or cod family, the pleuronects (halibut, turbot, &c), the herrings and mackerels are nowhere else in such abundance and excellence as on both sides of that ocean. In the tropics the large serrani (gropers) are a characteristic group. The bright-colored tropical fishes, such as cheto-donts and others, seem to be confined to the same limits as the corals, the coasts of America bathed by the equatorial current.
Large representatives of the mackerel tribe, the coryphm-na, improperly called dolphin, and the flying fishes, are the most common inhabitants of the high seas. - Of Crustacea peculiar to the Atlantic, the king or horseshoe crab of North America deserves mention, only one other species of the genus being known, in the Molucca islands. The mollusks are nearly all different in the Atlantic from those in the other oceans, even when so slender a barrier as the isthmus of Panama is interposed. In the Fue-gian and South African provinces alone is there a gradual merging through a common fauna with that of the Pacific and Indian oceans. Similar remarks might be made with regard to most of the radiates. Most of the known living crinoids inhabit the Atlantic. The corals are distributed altogether in accordance with the warm current. The W. coast of Africa, washed by comparatively cold currents, has scarcely any. The coast of South America, receiving warm water from the equatorial current, has a greater abundance, though their growth is checked by the fresh water and mud of the great rivers. But they flourish in the West Indies and as far north as Bermuda, under the influence of the Gulf stream and other warm water currents.
The West Indian coral fauna is destitute of true fungiae and of pocilliporcae, both so common in the Pacific. It has on the other hand a great abundance of gorgoniaceae (sea fans, sea feathers). - For ocean life at great depths, see Dredging.