268 Proceedings of the Royal Physical Society. 
stones.—To be brief, one may say that the limestones of 
marine origin are formed almost entirely by the direct and 
indirect agency of animal and vegetable organisms, living and 
dead. These, as Irvine has shown, extract their carbonate of 
lime chiefly from the sulphate of lime present in sea-water, 
from which, ultimately, they convert it into the carbonate. 
It will probably be generally admitted that all lime 
compounds in solution, both river-water and sea-water, were 
derived, primarily, from the silicates in eruptive rocks. 
From these they have been liberated by “ weathering,” and 
have been carried seaward in solution as_ bicarbonate. 
Probably nearly all limestones, except, perhaps, those 
associated with highly metamorphosed rocks of eruptive 
origin, are, so to speak, secondary products—the primary or 
initial stage of calcium being that of combination with silica 
in eruptive rocks. From both primary and secondary sources 
lime-salts are being carried seawards from the land by 
rivers at a rate which for the whole world is now fairly 
well known. 
It has to be remembered that it is mainly from this source 
that marine organisms obtain the supply whence the hard 
part of their calcareous structure is built up. Supposing, for 
the moment, that this lime secreted by marine organisms is 
wholly derived from the supply furnished by rivers, let us 
see what the quantity possible to obtain per annum upon the 
sea-bottom would be. For this purpose we must first review 
Dr John Murray’s figures relating to the relative areas con- 
cerned. Taking these from his latest papers, we have— 
Total Area of the Globe, . ‘ 5 196,940,700 square miles, 
Total Area of the Land, . 3 é 55,697,400 __,, me 
Total Area of Inland Drainage, . : 11,486,350 ,, 4 
Total Area of Ocean Drainage, . ° 44,211,050 ,, 9 
Area of Ocean Drainage to Area of entire Ocean, as 1 to 3'194. 
Area of Ocean Drainage to Area of Calcareous Deposits, 1 to 1°178. 
Area of Ocean Drainage to Area of Terrigenous Deposits, 1°62 to 1. 
Aver. percent. of CaCO, in 27,899,300 sq. miles of Terrigenous Deposits, 19° 
50,000,000 23 Deep Sea Clays, 6°7 
2,790, 400 n a Oozes, 4° 
10,420,600 rf Diatom Oozes, 22°96. 
