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then exist. We have ample proofs, from the every-day 
operation in our own furnaces, that the application of 
a violent heat to mixed mineral compounds alters their 
affinities to such an extent as to give rise to products 
of an entirely different character; such minerals as chalk, 
marble, or limestone rock, which consist of carbonic acid 
and lime, would lose that volatile acid at a high tem- 
perature, and caustic lime would be the result, as we 
find to be the case in the common process of burning. 
If, instead of heating the carbonate alone, we previously mix 
it with some of our sandstone, which consists principally of 
silica, we should not only expel the carbonic acid, as above 
stated, but a new compound, called silicate of lime, would be 
formed in its place. This decomposition is not confined to 
the carbonate of lime ; any other salt containing a volatile 
acid would be acted upon by silica at a high temperature 
in a similar manner ; hence we may fairly conclude that, 
during the igneous period just named, all the lime which 
now lies embedded in the form of limestone rocks, was 
then in the state of a silicate. Where, then, was the car- 
bonic acid which we now find mineralised with this lime to 
an extent beyond calculation? Chemistry teaches us that 
not only this, but all the carbon which now lies embedded 
in the form of coal, and all that existing in the vegetation 
which now clothes the surface of the earth, was originally 
in the state of carbonic acid gas, and must, consequently, 
have formed part of the then existing atmosphere. Hence 
we are bound to admit, that the quantity of carbonic acid 
in the atmosphere, before the deposition of the carboniferous 
rocks, and prior to the existence of vegetable or animal 
life, was considerably greater than at the present time. 
I can by no means reconcile myself to believing that the 
proportion extracted from the air during the deposition of the 
carboniferous series of rocks was so trivial as Liebig, in his 
