i877-J 
463 
in its Geological Relations. 
could have been no lack of carbonic acid ; and it becomes a 
matter of small difficulty to accept the theory that a retro- 
gressively greater proportion of carbonic acid gradually leads 
back to a primitive atmosphere in which that gas — as well 
as perhaps other gaseous acids, such as hydrochloric acid— 
was very abundant. 
In regard to this question as to the increase or decrease 
of carbonic acid, a variety of very interesting points suggest 
themselves, and the faCts almost altogether to range themselves 
on the side of a progressive decrease of carbonic acid. It 
seems certain that the amount of carbon stored up in the 
recesses of the earth very far exceeds that of the entire 
quantity combined as carbonic acid in the air. It is true 
that Liebig supposed the carbon so combined, which he 
calculated to reach 2800 billions of pounds, equal to about 
1,250,000,000,000 tons, — figures and tons will probably aid 
in a better conception of this enormous weight, — to be far 
in excess of all the carbon stored up in coal-beds, and in 
plants on and in the globe. But this will hardly be sub- 
scribed to when we remember that the coal of the British 
Isles alone, as estimated by the late Coal Commission, is 
about 195,000,000,000 tons (I have added about a third for 
waste, &c., deducted in the original estimate). The carbon 
in this will weigh about 146,000,000,000 tons, taking an 
average of 80 per cent. But this was only calculated for 
coals fit for use, of not less than 1 foot thickness, lying at 
no greater depth than 4000 feet. Now if we include all the 
coal of inferior quality, of less than 1 foot thick, and at 
greater depths than 4000 feet, and then throw into the 
balance the enormous supplies of coal of the rest of the 
world and of the older and newer formations, not to speak 
of the highly carbonaceous sbales, slates, schists, and clay 
ironstones, I think — even taking only this branch of the 
subject — we should rather be led to agree with Bischof, 
who, on the other hand, calculates that there is at least 
6620 times as much carbon in the earth as Liebig has esti- 
mated for the atmosphere;* and Bischof’s calculation is 
based on the very moderate assumption that the average 
proportion of carbon in- all rocks is at least 0*1 per cent, 
which he considers — and no doubt justly — -must fall far 
short of the real amount. This being so, it would certainly 
appear that there has been more carbon accumulated in the 
* Bischof, Cheni. Geology, vol. i., p. 204. Dr. Sterry Hunt has also esti- 
mated the amount of carbon secreted in the earth as far beyond that contained 
in the present atmosphere. 
