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Proceedings of Royal Society of Edinburgh . [sess. 
On the whole, however, the quantity of carbonate of lime that 
is secreted by animals must exceed what is re-dissolved by the 
action of sea water, and at the present time there is a vast accumu- 
lation of carbonate of lime going on in the ocean. It has been the 
same in the past, for with a few insignificant, exceptions all the 
carbonate of lime in the geological series of rocks has been secreted 
from sea water, and owes its origin to organisms in the same way as 
the carbon of the carboniferous formations ; the extent of these 
deposits appears to have increased from the earliest down to the 
present geological period. 
At the present time most of the carbonate of lime carried to the 
ocean by rivers has been directly derived from calcareous stratified 
rocks formed by organic agency in the sea in earlier geological ages, 
but the calcium in these formations was in the first instance derived 
from the decomposition of the lime-bearing silicates of the earth’s 
original crust, and this decomposition, which is still going on in the 
sea and on the land surfaces, is a continuous source of carbonate of 
lime. 
In considering the analyses showing the average composition of 
sea salts, one is struck with the relatively small quantity of those 
very substances which are extracted so largely from sea water by 
plants and animals, viz., carbonate of lime and silica. Siliceous 
deposits are of vast extent, yet silica occurs merely in traces in sea 
water ; carbonate of lime deposits are of vastly greater magnitude, 
yet carbonate of lime makes up only y-^th part of the saline consti- 
tuents of sea water, and only •g- g^t h part of the whole bulk of sea 
water. Sulphate of lime is ten times more abundant than the 
carbonate in sea water ; on the other hand, the river water that is 
poured into the ocean contains about ten times as much carbonate 
as it does of sulphate of lime.* 
The total amount of calcium in a cubic mile of sea water is esti- 
mated from analyses to be 1,941,000 tons, and the total amount of 
calcium in the whole ocean is calculated at 628,340,000,000,000 
tons. The total amount of calcium in a cubic mile of river water is 
estimated at 141,917 tons, and the total amount of this element 
carried into the ocean from all the rivers of the globe annually is 
* Murray, “ Total Annual Rainfall of the Globe,” Scottish Geog. Magazine , 
vol. iii. p. 65, 1887. ‘ 
