96 Mr. J. Stevenson on the Chemical and 



may be affected by volcanic action and caused to give up 

 their carbonic acid. Dr. Sterry Hunt calculated that there 

 was probably enough limestone on the earth to yield a 

 quantity of carbonic acid equal to 200 times the volume o£ 

 our present atmosphere. This quantity would be 700,000 

 times greater than the amount of carbonic acid at present 

 existing in the atmosphere. It would be about .'55,000,000 

 times greater than the amount annually decomposed by vege- 

 tation as calculated above, and of course would be very many 

 times greater than the difference between the amount annually 

 decomposed by vegetation and the amount annually restored 

 by the oxidation of organic remains. It is therefore quite 

 clear that there are ample stores to draw upon, and a simple 

 calculation will show that quite a limited area of country, 

 when subjected to volcanic action, may yield a large quantity 

 of carbonic acid. 



Ordinary limestone has the specific gravity 2*6, and there- 

 fore weighs 162 lbs. per cubic foot. It contains, if pure, 

 44 per cent, by weight of carbonic acid. A cubic mile of 

 limestone therefore contains 4686 X 10 6 tons carbonic acid, a 

 quantity which is roughly equal to fa of the amount that 

 we have calculated is annually removed from the atmosphere 

 by the growth of vegetation, and 470 cubic miles of lime- 

 stone contain an amount of carbonic acid equal to the total 

 carbonic acid of the atmosphere, viz. 2*2 x 10 12 tons. Now 

 the average aggregate thickness of limestone and other car- 

 bonates all over the earth must be about 1'64 miles in 

 order to contain the quantity of carbonic acid estimated by 

 Dr. Sterry Hunt ; and therefore, on the average, a surface 

 area of 286 square miles contains beneath it in the form of 

 limestone and other carbonates as much carbonic acid as there 

 is in the whole of the atmosphere. A region 100,000 square 

 miles in extent will contain, on the average, about 350 times 

 as much as the above quantity; and if subjected to volcanic 

 action, we may expect that a large proportion of this carbonic 

 acid will be evolved in the free condition. There is therefore 

 no difficulty in understanding that there is enough carbonic 

 acid of Volcanic or telluric origin to maintain the balance or 

 equilibrium between the amount of carbonic acid removed 

 from the atmosphere and the amount restored to it by the 

 various agencies already referred to. Further, it is obvious 

 from considerations regarding the erratic or intermittent 

 character of volcanic action generally, and also from consi- 

 derations regarding variations in the composition and dis- 

 tribution of rocks subjected to volcanic action, that there will 

 most probably be great variations in the amount of telluric 



