83 
ISLAND LIFE. 
[part I. 
oceanic mud should have been at once seized upon, and the 
conclusion arrived at that chalk is a deep-sea oceanic formation 
exactly analogous to that which has been shown to cover large 
areas of the Atlantic, Pacific, and Southern oceans. 
But there are several objections to this view which seem fatal 
to its acceptance. In the first place, no specimens of Globigerina- 
ooze from the deep ocean-bed yet examined agree even approxi- 
mately with chalk in chemical composition, only containing 
from 44 to 79 per cent, of carbonate of lime, with from 5 to 11 
per cent, of silica, and from 8 to 33 per cent, of alumina and 
oxide of iron. 1 Chalk, on the other hand, contains usually 
from 94 to 99 per cent, of carbonate of lime, and a very minute 
quantity of alumina and silica. This large proportion of car- 
bonate of lime implies some other source of this mineral, and 
it is probably to be found in the excessively fine mud produced 
by the decomposition and denudation of coral reefs. Mr. Dana, 
the geologist of the United States Exploring Expedition, found 
in the elevated coral reef of Oahu, one of the Sandwich Islands, 
a deposit closely resembling chalk in colour, texture, &c. ; while 
in several growing reefs a similar formation of modern chalk 
undistinguishable from the ancient, was observed. 2 Sir Charles 
1 Sir W. Thomson, Voyage of Challenger , Vol. II., p. 374. 
2 The following is the analysis of the chalk at Oahu: — 
Carbonate of Lime 92 800 per cent. 
Carbonate of Magnesia 2 -385 „ 
Alumina. 0 - 250 „ 
Oxide of Iron 0*543 , 
Silica 0*750 „ 
Phosphoric Acid and Fluorine 2-113 „ 
Water and loss 1-148 „ 
This chalk consists simply of comminuted corals and shells of the reef. 
It has been examined microscopically and found to be destitute of the 
minute organisms abounding in the chalk of England. ( Geology of the 
United States Exploring Expedition , p. 150.) 
This absence of Globigerince is a local phenomenon. They are quite 
absent in the Arafura Sea, and no Globigerina- ooze was found in any of 
the enclosed seas of the Pacific, but with these exceptions the Globigerince 
“ are really found all over the bottom of the ocean.” (Murray on Oceanic 
Deposits — Proceedings of Royal Society , Vol. XXIV., p. 523.) 
The above analysis shows a far closer resemblance to chalk than that 
of the Globigerina- ooze of the Atlantic, four specimens of which given by 
