352 T. S. Hunt— Chemical and Geological 
of carbon by the process of vegetable growth must therefore 
have liberated the same volume of oxygen’ Again, a stratum 
of carbonate of lime of specific gravity 2°7, covering the earth 
with a thickness of 8°69 metres, (or one of dolomite of sp. gr. 
2°85, and 758 meters thick) would contain an amount of car- 
bonie dioxide equal in weight to the present atmosphere.* 
t was in view of these processes that Ebelmen declared, in 
1846, that “the decomposition and the reproduction of certain 
mineral species very abundant on the surface of the globe cor- 
responds to important modifications in the composition of the 
atmosphere.” He farther said, “ Many circumstances tend to 
prove that in ancient geological periods the atmosphere was 
denser, and more rich in carbonic acid, and perhaps in oxygen, 
than at present. Toa greater weight of the atmospheric en- 
velop would correspond a stronger condensation of the solar 
year, page 135. 
We may get a clearer notion of the problem before us by 
a square mile of the earth’s crust cannot be less, and is proba- 
tation; the source of the original amount of carbon being; in 
his hypothesis, left unexplained. 
* T. Sterry Hunt on the Primeval Atmosphere, Proc. Amer. Assoc. Ady. Science, 
1866, and Can. Naturalist, IJ, iii, 118. 
er des Mines, IV, vii, 65; also Receuil des Trav. Scient. de M. Ebelmen, 
vol. ii, p. 55. 
t Nature, vol. xvi, p. 406. 
. 
