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Rh the existing are not the lineal descendants of the fossil types, the differences they present being not greater than may be fairly attributed to the prolonged action of differences of temperature, food, pressure, &c. And when these facts are taken in connection with those previously stated as to the probable remoteness of the period when (if ever) the present sea-bed of the Atlantic was dry land, the doctrine first put forth by Prof. Wyville Thomson, that there has been a continuous formation of Globigerina-mud on the bottom of the Atlantic from the Cretaceous epoch to the present time or, in other words, that the formation of chalk on the sea-bed of the Atlantic did not cease with the elevation of the European area, but has been going on through the whole Tertiary period, must be admitted as (to say the least) a not improbable hypothesis. That some considerable change took place at the conclusion of the Cretaceous epoch, by which the temperature of the upper stratum was lowered, so as to be no longer compatible with the existence of the fishes and chambered cephalopods characteristic of the Cretaceous fauna, may be fairly assumed from their disap pearance ; but this would not so much affect the deeper part of the basin, in which those lower types that seem more capable of adapting themselves to changes in external conditions would continue to hold their ground. That the like conditions had prevailed also through long previous geo logical periods, may be surmised from the persistence, over various parts of the Atlantic sea-bed, of the Apiocrinite type, which carries us back to the Oolitic formation, and of i the Pentacri,nus type, which has come down with very little i alteration from the Liassic ; whilst many existing Tere- bratulidce do not differ more from Oolitic types than the latter differ among each other. Going back still further, we find in the persistence of certain Foraminiferal types from the Carboniferous limestone to the present time, and in the character of its deep-sea beds, a strong indication that they originated in a Foraminiferal deposit, represent ing in all essential particulars that which is now going on ; while the persistence of the Lingula from the early j Silurian strata to the present time suggests the question I whether certain oceanic areas may not have remained in the condition of deep sea throughout the whole subsequent succession of geological changes.

BIBLIOGRAPHY. In addition to the ordinary sources of information, the following publications may be specially referred to for recent information in regard to the physical geography of the Atlantic : &quot; Reports of the Deep-Sea Explorations carried on inH.M. Steam-vessels Lightning/ Porcupine, and Shearwater, &quot; in Proceedings of Hie Roi/al Society for 1868, 1869, 1870, and 1872; &quot; On the Gibraltar Current, the Gulf Stream, and the General Oceanic Circula tion,&quot; in the Journal of the Royal Geographical Society for 1871; and &quot;Further Inquiries on Oceanic Circulation&quot; (containing a summary of the &quot; Challenger&quot; Temperature Survey of the Atlantic), in the same journal for 1874 ; Currents and Surface-Temperature of the North and South Atlantic, published by the Meteorological Committee ; and The Depths of the Sea, by Prof. Wyville Thomson. (W.B.C.)

 ATLANTIS,, or , an island men tioned by Plato and other classical writers, concerning the real existence of which many disputes have been raised. In the Timceus, Critias relates how his grandfather Critias had been told by Solon some remarkable events in early Athenian history which he had learned from the Egyptian priests at Sais, whose records went much further back than the native accounts. &quot; The most famous of all the Athenian exploits,&quot; Solon had been told, &quot;was the overthrow of the island Atlantis. This was a continent lying over against the pillars of Hercules, in extent greater than Libya and Asia put together, and was the passage to other islands and to another continent, of which the Mediter ranean Sea was only the harbour; and within the pillars the empire of Atlantis reached to Egypt and Tyrrhenia. This mighty power was arrayed against Egypt and Hellas and all the countries bordering on the Mediterranean. Then did your city bravely, and won renown over the whole earth. For at the peril of her own existence, and when the other Hellenes had deserted her, she repelled the invader, and of her own accord gave liberty to all the nations within the pillars. A little while afterwards there was a great earthquake, and your warrior race all sank into the earth ; and the great island of Atlantis also disappeared in the sea. This is the explanation of the shallows which are found in that part of the Atlantic ocean.&quot; (Jowett s Introduction to the Timccus.) Such is the main substance of the principal account of the island furnished by the ancients, an account which, if not entirely fictitious, belongs to the most nebulous region of history. The story may embody some popular legend, and the legend may have rested on certain historical circumstances; but what these were it is (as the numerous theories advanced on the subject may be held as proving) impossible now to determine.

 ATLAS ([Greek]), in Greek Mythology, called sometimes a son of Japetus and the nymph Asia, or of Uranus and Gaia, and at other times traced to a different parentage, but always known as the being -who supported on his shoulders the pillars on which the sky rested. He knew the depths of the sea (Odyssey, vii. 245), and in the first instance seems to have been a marine creation. The pillars which he supported were thought to rest in the sea, immediately beyond the most western horizon. But by the time of Herodotus (iv. 184), a mountain is suggested as best suited to hold up the heavens, and the name of Atlas is transferred to a hill in the N.W. of Africa. Then the name is traced to a king of that district, rich in flocks and herds, and owning the garden of the Hesperides. Finally, Atlas was explained as the name of a primitive astronomer. He was the father of the Pleiades and Hyades. Perseus encountered him when he searched for Medusa. Heracles took the burden of the sky from his shoulders, but cleverly contrived to replace it. Atlas bear ing up the heavens is mentioned as being represented on early works of art, e.g., on the chest of Cypselus (Pausan.,v. 18,1), j and on the throne of Apollo at Amyclse (Pausan., iii. 18, 7) ; and this subject occurs on several existing works of art.

 ATLAS, a mountain-chain of Northern Africa, between the great desert of the Sahara and the Mediterranean. The range has been but partially explored, and geographers differ as to its extent, some considering it to reach from Cape Ghir i on the Atlantic to Cape Bon, the north-east point of Tunis, i while others include under the name the whole mountain j system between Cape Nun and the greater Syrtis. In i this latter sense it forms the mountain-land of the countries of Marocco, Algeria, Tunis, and Tripoli. It is composed of ranges and groups of mountains, enclosing well-watered and fertile valleys and plains, and having a general direction from W. to E. The highest peaks are supposed to attain an elevation of nearly 15,000 feet; and although none of them reach the height of perpetual snow, some of their loftiest summits are covered with snow during the greater part of the year. Mount Miltsin, 27 miles S.E. of the city of Marocco, was ascertained by Captain Wash ington to be 11,400 feet high. The greatest heights are in^Marocco, from which point they appear to diminish in 