FVPOIM SIS OF CAUSE OF GLACIAL. PERIODS. 2083 
pertinent to the discussion, if the foregoing doctrine relative to 
the mode of action of the ocean during a glacial period is 
correct, for it is there maintained that the ocean does not give 
up its carbonic acid with increasing depletion of the atmosphere, 
but, on the contrary, increases its content. They have some 
interest, however, in connection with it and with other phases of 
the atmospheric hypothesis which the reader may possibly wish 
to consider. They also have some pertinency to the discussion 
of Paleozoic glaciation, to be taken up presently. 
We are here concerned especially with the rate at which 
atmospheric carbonic acid may be consumed to the amount of 
one half the total content. For convenience, no account has 
been taken of the return of carbonic acid from the ocean or 
through organic action. We reach the rather startling result 
that if there were no return, the decomposing and solvent action 
on the present contact area would consume one half of the 
atmospheric carbon dioxide in less than 1000 years. This 
result, based on Reade’s estimate, may be checked by independ- 
ent computation on a more familiar basis and by different modes 
of computation. For example, by assuming the average rate of 
degradation of the land surface to be one foot in 5000 years, 
and that the carbonates constitute 15 per cent. of the material 
removed, one half of the carbonic acid of the atmosphere would 
be consumed in 1248 years, if there were no return; or in 1000 
years if the degradation was one foot in 4000 years. 
The actual depletion must, of course, depend upon the excess 
of this rate of removal over the rate of return. I have already 
endeavored to show that there was a very large fluctuation in the 
conditions that determined the relative rates of consumption and 
return, notably that the land of the Ozarkian time was more 
than 20 per cent. greater in area than the present land, and that 
its elevation was probably 100 per cent. or 200 per cent. greater 
at the maximum stage of protrusion. And this was correlated 
with codperating conditions in the ocean. Both of these esti- 
mates, however, must be considerably reduced to give a safe 
measure of the area which was operative at the time of the 
