THREE CRUISES OF THE “ BLAKE.” 
148 
than in a true oceanic area.” t There is no proof that massive 
formations are deposited anywhere except, along continental 
shelves, while at the greatest depth we may find the true red 
clay, the result of chemical decomposition. 
Mr. J.S. Gardner considers the blue mud found around shores 
and in partially closed seas, and passing into a deep-sea deposit 
at a distance from land, as the equivalent of the gault. The 
gault has among its mollusca, Leda, Limopsis, and Denta- 
lium, all well-known deep-sea mollusca. Its foraminifera and 
echinoderms likewise are deep-water types. The upper gault 
represents a deeper sea ; blue muds are replaced by green muds; 
from that we pass to chalk marl, which is apparently a sort of 
globigerina ooze, and finally to the white chalk, with its great 
extent and thickness, which proclaim it to be an oceanic or a 
deep-water deposit; and there seems to be nothing with which 
it can be compared except globigerina ooze. 
Professor Liversidge describes a chalk formation from New 
Zealand, consisting of eighty-one per cent of carbonate of lime 
and seven per cent of silica. This contains, as is stated by 
Brady, species of foraminifera now found in deep-sea specimens 
of globigerina ooze from fifteen hundred to two thousand fath- 
oms in depth in the South Pacific. The origin of the New 
Britain chalk is not known, but it is probably recent; the speci- 
mens are thrown up on beaches after storms. White chalk con- 
tains ninety-eight per cent of carbonate of lime, and gray chalk 
ninety-four per cent. The “Blake” also dredged off Nuevitas, 
in 994 fathoms, recent chalk which Murray says is more like 
white chalk than anything he has seen. 
Chalk is certainly not derived from the disintegration of coral 
reefs, although we frequently find patches of rock associated 
with coral reefs closely resembling true chalk, both in texture 
and composition, — as, for instance, in the so-called modern 
chalk of Oahu. The percentage of carbonate of lime com- 
posing reef corals? varies from ninety-five to ninety-eight ; this 
1 
. 1 Chalk may be forming at very great ? Sharples gives the following per- 
depths close to a continent. See the an- centages of carbonate of lime: Ocu- 
alysis of the modern chalk collected off lina, 95.37 ; Manicina, 96 54 ; Madrepora, 
Nuevitas in 994 fathoms. (Murray, Bull. 97.19; Siderastrea, 97.30; Millepora, 
M. C. Z. XII., No. 2.) : 
97.46 ; Agaricia, 97.73. Madrepora pal- 
