The area over which the white chalk preserves a nearly homogeneous aspect is so vast, that the earlier geologists despaired of discovering any analogous deposits of recent date. Pure chalk, of nearly uniform aspect and composition, is met with in a north-west and south-east direction, from the north of Ireland to the Crimea, a distance of about 1140 geographical miles, and in an opposite direction it extends from the south of Sweden to the south of Bordeaux, a distance of about 840 geographical miles. In Southern Russia, according to Sir R. Murchison, it is sometimes 600 feet thick, and retains the same mineral character as in France and England, with the same fossils, including _Inoceramus Cuvieri, Belemnitella mucronata,_ and _Ostrea vesicularis_ (Fig. 251). Diagrammatic section from Hertfordshire, in England, to Sens, in France. Great light has recently been thrown upon the origin of the unconsolidated white chalk by the deep soundings made in the North Atlantic, previous to laying down, in 1858, the electric telegraph between Ireland and Newfoundland. At depths sometimes exceeding two miles, the mud forming the floor of the ocean was found, by Professor Huxley, to be almost entirely composed (more than nineteen-twentieths of the whole) of minute Rhizopods, or foraminiferous shells of the genus Globigerina, especially the species _Globigerina bulloides_ (see Fig. 232.) the organic bodies next in quantity were the siliceous shells called _ Polycystineæ,_ and next to them the siliceous skeletons of plants called _Diatomaceæ_ (Figs. 233, 234, 235), and occasionally some siliceous spiculæ of sponges (Fig. 236) were intermixed. These were connected by a mass of living gelatinous matter to which he has given the name of _Bathybius,_ and which contains abundance of very minute bodies termed Coccoliths and Coccospheres, which have also been detected fossil in chalk. Sir Leopold MacClintock and Dr. Wallich have ascertained that 95 per cent of the mud of a large part of the North Atlantic consists of Globigerina shells. But Captain Bullock, R.N., lately brought up from the enormous depth of 16,860 feet a white, viscid, chalky mud, wholly devoid of Globigerinæ. This mud was perfectly homogeneous in composition, and contained no organic remains visible to the naked eye. Mr. Etheridge, however, has ascertained by microscopical examination that it is made up of _ Coccoliths, Discoliths,_ and other minute fossils like those of the Chalk classed by Huxley as _Bathybius,_ when this term is used in its widest sense. This mud, more than three miles deep, was dredged up in latitude 20° 19′ N., longitude 4° 36′ E., or about midway between Madeira and the Cape of Good Hope. Fig. 232: Globigerina bulloides, Calcareous Rhizopod. Fig. 233: Actinocyclus, Fig. 234: Pinnularia, Fig. 235: Eunotia bidens, Siliceous Diatomaceæ. Fig. 236: Spicula of sponge, Siliceous sponge.