356 T. 8. Hunt—Chemical and Geological 
thought and investigation, it may be said, lead to the conclu- 
sion that the seat of volcanic phenomena is to be found in sedi- 
mentary strata,* and that although the earth’s interior inter-. 
venes as a source of heat, the carbonic dioxide disengag 
from its crust is derived, as in the first hypothesis mentioned 
by Ebelmen, from the decomposition of carbonates previously 
generated by sub-aerial reactions. 
The problem still before us is then to find the source of the 
vast amount of carbonic dioxide continuously supplied to the 
atmosphere throughout the geologic ages, and as continuously 
removed therefrom, and fixed in the form of carbonaceous 
* Tbid, pp. 59-67. 
