WHITE CHALK. 
■ 287 
The area over which the white chalk preserves a nearly 
homogeneous aspect is so vast, that the earlier geologists de¬ 
spaired 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 vesicula- 
ris (Fig. 251, p. 295). 
Great light has recently been thrown upon 
the origin of the unconsolidated white chall? 
by the deep soundings made in the North At¬ 
lantic, previous to laying down, in 1858, the 
electric telegraph between Ireland and New¬ 
foundland. 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 Glohige- 
rina^ especially the species Glohigerina hul- 
loides (see Fig. 232). The organic bodies 
next in quantity were the siliceous shells 
called Polycystinem^ and next to them the 
siliceous skeletons of plants called Diatoma- 
cece (Figs. 233, 234, 235), and occasionally 
some siliceous spiculse of sponges (Fig. 236) 
were intermixed. These were connected by 
a mass of living gelatinous matter to which 
he has given the name of JBathyhms^ 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 Glofcgerina shells. But Capt. Bullock, R. N., lately 
brought up from the enormous depth of 16,860 feet a white, 
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