1890-91.] Dr Murray and Mr Irvine on Silica in Seas. 
229 
On Silica and the Siliceous Remains of Organisms in 
Modern Seas. By John Murray, LL.D., Ph.D., &c., 
and Robert Irvine, F.C.S. 
(Read March 16, 1891.) 
In a former paper to this Society, we pointed out the important 
role played by carbonic acid in modern seas, with special reference 
to the vast deposits of carbonate of lime now taking place in coral 
reefs and those other calcareous deposits known as Globigerina and 
Pteropod Oozes. It was pointed out that carbonic acid was the 
chief agent in the disintegration of felspars and other silicates of 
the earth’s surface, that it was concerned in all the changes that 
result in the secretion of carbonate of lime by marine organisms 
from any of the lime salts in sea-water, that a vast amount of car- 
bonic acid was being locked up in the calcareous deposits now in 
process of formation on the sea-bed, and that there was an accumu- 
lation of these calcareous deposits chiefly towards the equatorial 
regions of the ocean basins. In the present paper we propose to 
deal with the great antagonistic power to carbonic acid, viz., silica, 
and with the siliceous organic remains in the ocean. 
Silica, or silicic acid, is an oxide of silicon, indeed the only oxide 
of that element known to exist, and resembles in many of its pro- 
perties the oxide of carbon (carbonic acid) ; it is probably the 
widely distributed body in the surface and subsurface layers of 
the earth’s crust. When the earth’s surface was at a high tempera- 
ture, probably all the silica was in combination with lime, magnesia, 
iron, alumina, and alkalies — forming the great series of silicates. 
At a high temperature silica has a great affinity for bases, but at a 
low temperature it is in most cases replaced by carbonic acid from 
its compounds. It thus happens that from early geological times 
carbonic acid has been extracted from the atmosphere, and locked 
up in the solid crust of the earth. If this process goes on without 
limitatiou life will ultimately become impossible on the earth’s sur- 
face. From volcanoes and fissures carbonic acid is given off, owing, 
apparently, to the silica again taking the place of the carbonic acid 
in the heated rocks below. In all the ordinary disintegrating pro- 
vol. xviii. 20/5/91 
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