JoLY — An Estimate of the Geological Age of the Earth. 37 



condition would result in "the conversion of all carbonates, chlorides, and sul- 

 phates into silicates ; and the separation of the carbon, chlorine, and sulphur in 

 the form of acid gases, which, with nitrogen, watery vapour, and a probable excess 

 of oxygen, would form the dense primeval atmosphere."* 



That sulphuric acid existed in the early atmosphere and hydrosphere in, at least, 

 relatively small quantities, is more than probable. In the sea-salts of to-day it 

 forms a relatively small part, and is being supplied by the rivers at a rate which, 

 acting over geological time, is far more than sufficient to account for all that is in it. t 

 It is being constantly thrown down upon the ocean floor in the form of 

 calcium sulphate ; constituting about 0-7 per cent, of the red clay, and 0-4 per 

 cent, of the Radiolarian ooze, 0'3 per cent, of the Diatom ooze, and about 0*8 per 

 cent, of the Globigerina ooze, as well as entering into other extensive floor-deposits 

 of the ocean. Sulphur exists, according to Clarke, as a constituent of the funda- 

 mental crust, amounting to 0-06 per cent. We find then not only a source of 

 supply in the rocks, but an annual river supply more than adequate to account 

 for what is in the ocean. We cannot, therefore, fairly make allowance for its 

 solvent action in early times. If free, it probably existed in relatively minute 

 quantities. 



In the case of carbonic acid we can effect a fairly satisfactory estimate of its 

 amount from the volume of limestone rocks now on the Earth's surface ; but in 

 the case of this acid we find a much less energetic body than hydrochloric acid. 

 Its activity has i^robably extended all through geological time, and its gradual 

 absorption been marked by the limestones of all ages. We must bear in mind, 

 however, what has frequently been pointed out — that the volcanic extrusion of 

 this substance throughout geological time has probably been considerable. 



The only warranted correction of large amount appears, then, to be that due 

 to the attack upon the early rocks by the hydrochloric acid. We make a 

 deduction of 12"5 millions of years for the primeval salinity of the ocean brought 

 about by this means. It is, however, evident that the solution of this amount of 

 material was not effected instantaneously, but by an accelerated denudation, 

 extending over some period of time, the duration of which, we can satisfy 

 ourselves, however, is nearly negligible. A rough estimate of the amount of 

 denudation, as a layer of rock removed from the whole terrestrial land surface, 

 is easily arrived at. 



We have already found, in fact, that 1972 x 10'^ tons of sodium must, 

 roughly, have been dissolved out of the primeval rocks. In Clarke's table of the 



* " Chemical and Geological Essays," 1897, p. 40. 



f The annual river supply of the element sulphur is ahout 124 x 10* tons, and the mass of S in the 

 ocean is ahout 12 x 10'^ tons. A part of the sulphates of the rivers is derived from rain, and hence from 

 the sea. 



