32 Proceedings of the Ohio State Academy of Science 



greater thickness of the zone of weathering, the ground water 

 level being lowered as streams deepen their valleys, following the 

 uplift. The abstraction of COg from the air in the process of 

 changing carbonates to bicarbonates which acconiDanies the 

 chemical weathering of limestones, and in the formation of car- 

 bonates by combination with the oxides of calcium, potassium and 

 sodium in igneous and metamorphic rocks, is the primary cause 

 of colder climates which bring on glaciation. The diminished 

 area of the continental shelf which follows uplift, with the con- 

 sequent lessening of lime-secreting organisms, would mean less 

 COo returned to the water and air, as a result of changing the 

 bi-carbonate of lime to the carbonate in shell making. The gen- 

 eral theory has conseauences in a number of directions which 

 cannot be followed here. 



The recurrent glaciations are explained as due to the com- 

 bination of primary and secondary causes pushing their effects 

 beyond a condition of equilibrium, so that a reaction ensues, 

 bringing on the milder conditions of an interglacial epoch, the 

 conditions swinging to one side or the other of a mean until the 

 general cause has worked out its effect. 



The peculiar localization of Pleistocene continental glaciation 

 in North /\merica and Northwestern Europe is attributed to the 

 control of the great area of low atmospheric pressure located 

 over the North Atlantic, upon the winds of the two northern con- 

 tinents. 



This statement is wholly inadequate as a description of the 

 atmospheric hypothesis. But I am not attempting to describe 

 that hypothesis fully. I have not time to do that, and it would 

 not accord with the purpose of this paper. But I think I have 

 said enough to indicate in general the kinds of agencies which 

 Chamberlin believes were responsible for glaciation. They are 

 fundamentally atmospheric, changes in the amount of COo in the 

 atmosphere. The cause of these changes was geologic, land up- 

 lift followed by erosion and weathering. The theory is proposed 

 as a working hypothesis. It has been elaborated in great detail 

 by its author. It seems to be a better exolanation of glaciation 

 and of glacial history than any of its predecessors, but it may 



