Ppa NEUEN OMGREAT EPOCHS OF LIMESTONE 
PORMALION URONS DEE CONSTIDULTION OF DEAE 
ATMOSPHERE. 
THE virtues of carbon dioxide are in inverse ratio to the 
sinister reputation which ‘a little knowledge” and a narrow 
homocentric point of view have given it. As a constituent of 
the atmosphere it is as necessary to the maintenance of life as 
oxygen because it is the food of plants and they in turn are the 
food of animals. Its peculiar competency to retain the heat of 
the sun renders it a decisive factor in the maintenance of that 
measurable constancy and geniality of temperature upon which 
the existence of life depends. It is a leading agency in the 
disintegration of crystalline rock and is a necessary factor in 
other geologic changes. It is an essential link in a chain of 
vital processes which involve all the constituents of the atmos 
phere. Inherently it may be no more necessary to these proc- 
esses, Save in its thermal nature, than is oxygen, but being the 
minimum factor in the atmosphere it becomes regulative and deci- 
sive, because variations in it affect the whole cycle of processes 
dependent on it, while similar variations in the major constitu- 
ents may have no appreciable effect. It is the east chemical 
constituent of a mixture that determines the amount of reaction. 
A loss of nitrogen or oxygen equal to .0003 of the atmosphere 
would doubtless be wholly inconsequential, while that amount 
of loss of carbon dioxide would be fatal to life and to many 
important geologic processes. Oxygen would doubtless become 
the critical factor if geologic processes in the aggregate con- 
sumed it more rapidly than they do carbonic acid. But the 
reverse seems to be the case now, and it has quite certainly 
been the case throughout the determinable portion of geologic 
history. This becomes equally apparent whether we approach 
the question in the order of the actual processes or the reverse. 
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