HNPOLHMESTS OL SCAUSE OF (GLACIAL, PERIODS 677 
uncovered area would be renewed. This, of course, would begin 
so soon as the retreat began, and increase in a corresponding 
measure; but it is a slow process, while the reactions of the 
ocean are relatively rapid —indeed they should keep close pace 
with the rise of temperature which they induce. There should 
be no appreciable lag. After the retreat of the ice a new sur- 
ficial factor would come into play, the sheet of drift spread over 
the:suttace. (In)so far as this consisted, of wndecomposable 
matter blanketing decomposable matter, it would interfere with 
the progress of decomposition, but in so far as it consisted of 
limestones and silicates ground to a flour and exposed to the 
atmosphere, it would facilitate chemical action and expedite a 
second depletion of the atmosphere and through it a second 
term of glaciation. Aside from the effects of this mantle of 
drift and such changes of topography as might have occurred, 
the conditions for the renewal of glaciation would be, so far as 
I see, as effective as they were at the outset. Assuming that 
they were equal to the preceding, a second glaciation equal to 
the first is to be postulated, and a corresponding reaction at 
length, as in the previous case, due to like agencies. Thus a 
series of glaciations and deglaciations should follow each other 
until the general causes lying back of glaciation had disap- 
peared. 
In so far as the land, on the whole, settled back toward sea 
level or was worn away, or, by any other agency, lost its degree 
of effective ‘exposure to ‘the atmospheric action, in so far the 
conditions of glaciation would disappear. Pursuing the normal 
history which follows a period of great land elevation, it is to be 
presumed that there would be a gradual reduction of the land 
surface and land elevation, and that hence the conditions pro- 
ductive of glaciation would gradually pass away. On such an 
assumption it is presumed that the recurrent glacial advances and 
retreats would become more and more feeble until the series van- 
ished. Nominally, then, the glacial and interglacial epochs 
should form a rhythmical series declining from large oscillations 
at the maximum to lesser and lesser oscillations as the series 
