158 Scientifie Proceedings, Royal Dublin Society. 
The only agency of a different kind, 7.e. one tending to per- 
manently increase the amount of aerial carbonic anhydride (and 
so to disturb the balance maintained by the organic world) is to be 
found—so far as we are aware——in volcanic or subterranean 
sources, which in the past may have been of enormous importance, 
but of which the record only remains geologically. 
We shall allude presently to the curious theory of Ebelmen, 
Sterry Hunt, and Winchel, who supposed that vast quantities of 
carbonic anhydride have reached the earth from inter-planetary 
space. 
Opposed to the sources of evolution are those agencies 
acting in the opposite direction, 7.e. as ‘‘ sources of absorption.” 
These have acted in the past, are still active, and will, no doubt, 
continue in action—not only tending to remove carbonic anhy- 
dride from the atmosphere, but also to permanently withdraw it 
from the sphere of organic action. The first of these consists in 
the weathering of rocks, whereby broadly speaking, silicates 
become replaced by carbonates. ‘To this action the production of 
soil is due, and to it also may be traced the gradual disintegration 
of mountain peaks and the general levelling of the earth’s surface 
which is no doubtoceurring. While this action is of apurely mineral 
nature, the second source of absorption is of a totally different 
kind, and is the work of the animal kingdom. Animals having a 
calcareous coating or skeleton, such as mollusks, corals, foraminifera, 
&¢c., have in all probability derived the carbonic anhydride of their 
calcareous material, if not immediately, at least ultimately, from the 
air. ‘The vast geological strata of cretaceous substances which owe 
their origin to this cause are silent but impressive witnesses to the 
enormous quantities of carbonic anhydride thus locked up, and, as 
far as can be judged, permanently removed from the sphere of 
organic action.’ 
Three distinct sets of actions are thus occurring in nature 
which affect the amount of atmospheric carbonic anhydride. First 
come those sources of evolution tending to permanently increase 
it; next, those of absorption causing the opposite effect; and, 
lastly, regulating actions in which evolution and absorption occur 
1 Broadly speaking, at all events as some slight evolution may occur by the action 
of the acids present in vegetable goil on the carbonates contained in it. 
