G04 
ELEMENTS OF GEOLOGY. 
acid and lime from the materials which it reduces to fusion 
or semi-fusion, only carbonate of lime, but also free 
carbonic acid gas, is given off plentifully from the soil and 
crevices of rock^s in regions of active and spent volcanoes, as 
near ^^aples and in Auvergne. By this process, fossil shells 
or corals may often lose their carbonic acid, and the residual 
lime may enter into the composition of augite, hornblende, 
garnet, and other hypogene minerals. Although we can not 
descend into the subterranean regions where volcanic heat is 
developed, we can observe in regions of extinct volcanoes, 
such as Auvergne and Tuscany, hundreds of springs, both 
cold and thermal, flowing out from granite and other rocks, 
and having their waters plentifully charged with carbonate 
of lime. 
If all the calcareous matter transferred in the course of 
ages by these and thousands of other springs from the lower 
part of the earth’s crust to the atmosphere could be present¬ 
ed to us in a solid form, we should find that its volume was 
comparable to that of many a chain of hills. Calcareous 
matter is poured into lakes and the ocean by a thousand 
springs and rivers; so that part of almost every new calca¬ 
reous rock chemically precipitated, and of many reefs of shel¬ 
ly and coralline stone, must be derived from mineral matter 
subtracted by plutonic agency, and driven up by gas and 
steam from fused and heated rocks in the bowels of the 
earth. 
The scarcity of limestone in many extensive regions of 
metamorphic rocks, as in the Eastern and Southern Grampi¬ 
ans of Scotland, may have been the result of some action of 
this kind; and if the limestones of the Lower Laurentian in 
Canada afford a remarkable exception to the general rule, 
we must not forget that it is precisely in this most ancient 
formation that the Eozoon Canadense has been found. The 
fact that some distinct bands of limestone from VOO to 1500 
feet thick occur here, may be connected with the escape from 
destruction of some few traces of organic life, even in a rock 
in which metamorphic action has gone so far as to produce 
serpentine, augite, and other minerals found largely inter¬ 
mixed with the carbonate of lime. 
