150 CORAL FORMATIONS. 
sparing diffusion of animal life in the seas about whose shores they 
may have been formed. If this destruction of fossils is so complete 
when the sands are of limestone, much more rapid and thorough 
should it be when they are siliceous. As the sea by its action bears 
off the finer material, and leaves only what is in the condition of sand 
or a coarser material, the carbonate of lime of fossils might be almost 
wholly removed from among siliceous sands, and hardly a trace re- 
main which the chemist could detect. 
VI. The formation of chalk from coral is known to be exemplified 
at only one spot among the reefs of the Pacific. The coral mud de- 
scribed appears to be a fit material for its production ; and when dried 
it takes much the appearance of chalk. ‘This fact was pointed out by 
Mr. Darwin, and was suggested to the writer by the mud in the lagoon 
of Honden Island. Still it does not explain the main point; for under 
all ordinary circumstances, this mud solidifies into compact limestone, 
instead of chalk. This appears, moreover, to be the result which 
should be expected. What condition then is necessary to vary the 
result, and set aside the ordinary process? 
The bed of chalk referred to was not found on any of the coral 
islands, but in the elevated reef of Oahu, of which reef it formed a 
constituent part. It is twenty or thirty feet in extent, and eight or 
ten deep. The rock could not be distinguished from much of the 
chalk of England: it is equally fine and even in its texture, as earthy 
in its fracture, and so soft as to be used on the blackboard in the 
native schools. Some imbedded shells look precisely like chalk fossils. 
It consists, according to an analysis by Prof. B. Silliman, Jr., of 
Carbonate of lime - - - - - - 92°800 
Carbonate of magnesia - - - - - 2°385 
Alumina - - - - - - - 0°250 
Oxyd of iron - - - - : : 0°543 
Silica - - - - - - - 0-750 
Phosphoric acid and fluorine - : - - 2:113 
Water and loss - ° - - - - 1:148 
The locality is situated on the shores just above high tide level, 
near the foot of Diamond Hill. This hill is an extinct tufa cone, near 
seven hundred feet in height, which rises from the water’s edge, and in 
its origin must have been partly submarine. It is one of the lateral 
cones of eastern Oahu, and was thrown up at the time of an eruption 
through a fissure, the lavas of which appear at the base. There was 
