HVPOTHESIS OF CAUSE OF GLACIAL PERIODS 671 
phases. The salient effect of this, reasoning on general prin- 
ciples, must be to push results to an extreme from which reac- 
tion is inevitable. Let us consider this in detail. It is thought 
that there were three dominant agencies concerned in this, 
modified by several subsidiary ones. 
1. A necessary consequence of the accelerated rate of trans- 
mission of carbon dioxide to the sea, combined with a slackened 
rate of release in the sea, was an accumulation of oceanic carbon 
dioxide. The primary form of this was an increase of the car- 
bonates. 
2. The cooling of the sea waters which attended the process 
reduced the dissociation, and hence the carbonates were more 
nearly full bicarbonates than before. There were, therefore, not 
only more carbonates, measured by the bases, but they carried more 
carbon dioxide in proportion to the bases. 
3. With the growth of the snow-fields attendant on the 
progress of glaciation, there was an increase of reflection of the 
sun’s radiation and a reduction of its absorption. Computation 
shows that the albedo is an important factor. 
Subsidiary to these there were the following: 
4. There was an increase in the absorption of carbonic acid 
in the ocean, resulting from the lowering of the temperature. 
This, however, was offset by the declining partial pressure of the 
carbon dioxide in the air, and, as the two seem to be of the 
same order of magnitude, they may be set aside for the present. 
5. With increasing cold there was a less rapid decay of 
organic matter and a less compiete release of carbon dioxide. 
Over against this, however, there was a reduction in the amount 
of carbon locked up in living organic matter. It is difficult to 
form a trustworthy estimate of either, but it may be provisionally 
assumed that they belong to the same order of magnitude and 
may be set aside together. At any rate, any residual difference 
would not apparently be a notable factor. 
6. The majority of chemical authorities state that the solu- 
bility of calcium carbonate in water saturated with carbonic acid 
increases with a lowering of temperature through ordinary 
