162 Scientific Proceedings, Royal Dublin Society. 
May not the permanent regulators of atmospheric carbonic 
anhydride in the past, at all events, be found in those mineral 
and animal agencies which have led to the absorption of the gas 
and the formation of calcareous deposits P 
No doubt the reciprocal action of plant and animal life on air 
and the regulating action of the oceans may possibly be adequate 
instruments for maintaining a state of balance or equilibrium in 
the amount of atmospheric carbonic anhydride, and for the circu- 
lation of the carbon necessary for the existence of the organic 
world, provided that no additional and considerable sources of absorp- 
tion or evolution are active. But such is not the case as we have 
seen. Therefore we suggest that the chief permanent source of 
evolution, viz. volcanie or subterranean action, is met and com- 
pensated by the chief permanent sources of absorption, ¢.e. the 
weathering of rocks with the formation of earthy carbonates, and 
the eventual absorption of these by ‘“‘cretaceous’’ organisms, 
while a certain proportion of carbonic anhydride remains free in 
the air to be dealt with by plants and animals. 
The production of coal may point to an effort of nature in the 
past to reduce the proportion of atmospheric carbonic anhydride 
by thus temporarily locking up the carbon, the amount of the 
former having become excessive with a correlative preponderance 
or luxuriance of vegetable life. 
May we not be entering upon a period when the reverse is 
occurring with absorption and diminution of aerial carbonic 
anhydride, in spite of our unconscious efforts to increase its amount 
by the combustion of coal and petroleum—a period which may 
foreshadow the complete extinction of life on our globe ? 
Several memoirs bearing on the subject just discussed deserve 
mention. 
In a series of papers, published in the ‘‘ Chemical News,” 
I’. Li. Phipson! discusses the question of the primeval atmosphere, 
and the changes which have subsequently occurred in its com- 
position. 
He bases his views on a theory propounded, he says, by Keone, 
according to which the carbonic anhydride and nitrogen of the air 
have never ceased diminishing since the origin of living creatures 
1 Phipson. Chemical News, vols. 67, 68, 70. 
