INFLUENCE OF LIMESTONE UPON THE ATMOSPHERE 613 
probably does not exceed two or three times the amount held 
in the atmosphere. If we assume these figures to be approxi- 
mately correct there remains, in a semi-fixed or loose condition, 
carbon dioxide to the amount of fifteen or sixteen times the 
present normal content of the atmosphere. This large reserve 
of carbon dioxide is the radical factor in this discussion. 
Let a status of land and water and of atmosphere and ocean, 
such as now exist, be assumed. Since a certain amount of car- 
bon dioxide is associated with the monocarbonate of lime in 
solution as the second or bicarbonating equivalent, and since 
the secretion and deposition of the lime takes place as the 
monocarbonate, the associated carbon dioxide is set free. The 
deposition of limestone is, therefore, a process of conversion of 
semi-fixed carbon dioxide into free carbon dioxide. This free 
carbon dioxide under the law of diffusion distributes itself 
through the ocean and the atmosphere according to the 
demands of tensional equilibrium, The ocean and the atmos- 
phere are thereby alike enriched in carbonic acid. If this 
process were continued without reciprocal action of the opposite 
kind, the ocean would in time be exhausted of its calcium 
bicarbonate and the semi-fixed factor would all become free. 
But as elsewhere urged* the disintegration of crystalline 
rock through the agency of the atmosphere consumes carbon 
dioxide in the carbonation of the alkalis and alkaline earths 
contained in them.? _In particular, the calcium silicates of the 
crystalline rocks become calcium bicarbonate and are in part car- 
ried in solution down to the ocean. Over against the liberating 
function of lime-deposition, therefore, there is set this reciprocal 
process of fixation. Over against the enrichment of the atmos- 
phere in carbon dioxide due to the former there is a depletion 
due to the latter. Now if these two processes were in perfect 
balance, a static condition of the atmosphere,so far as these 
factors are concerned, would be maintained. It is, however, 
*A Group of Hypotheses Bearing on Climatic Changes, Jour. GEOL., Vol. V, 
No. 7, October-November, 1897. 
? The organic cycle and other processes affect the supply and loss of carbonic 
acid concurrently, but they are purposely omitted here for simplicity’s sake. 
