320 C. Schuchert — Evolution of Geologic Climates. 



Art. XX. — Evolution of Geologic Climates; by Charles 



Schuchert. 



Under the above title, F. H, Knowlton has written a 

 most interesting paper/ the thesis of which is the follow- 

 ing: 



''Relative uniformity, mildness, and comparative equability of 

 climate, accompanied by high humidit}^, have prevailed over the 

 greater part of the earth, extending to, or into, polar circles, dur- 

 ing the greater part of geologic time — since, at least, the Middle 

 Paleozoic. This is the regular, the ordinary, the normal condi- 

 tion" (p. 501). 



In another place we read : 



"B}^ many it is thought that one of the strongest arguments 

 against a gradually cooling globe and a humid, non-zonally dis- 

 posed climate in the ages before the Pleistocene is the discovery of 

 evidences of glacial action practically throughout the entire geo- 

 logic column. Hardly less than a dozen of these are now known, 

 ranging in age from Huronian to Eocene. It seems to be a very 

 general assumption by those who hold this view that these evi- 

 dences of glacial activities are to be classed as ice ages, largely 

 comparable in effect and extent to the Pleistocene refrigeration, 

 but as a matter of fact only three are apparently of a magnitude 

 to warrant such designation. These are the Huronian glaciation, 

 that of the 'Permo-Carboniferous, ' and that of the Pleistocene. 

 The others, so far as available data go, appear to be explainable 

 as more or less local manifestations that had no widespread effect 

 on, for instance, ocean temperatures, distribution of life, et cet- 

 era. They might well have been of the type of ordinary moun- 

 tain glaciers, due entirelv to local elevation and precipitation" 

 (pp. 547-548). 



And again: 



"If the sun had been the principal source of heat in pre-Pleis- 

 tocene time, terrestrial temperatures would of necessity have been 

 disposed in zones, whereas the whole trend of this paper has been 

 the presentation of proof that these temperatures were distinctly 

 non-zonal. Therefore it seems to follow that the sun — at least 

 the present small-angle sun — could not have been the sole or even 

 the principal source of heat that warmed the early oceans" (p. 

 547). 



Doctor Knowlton naturally lays greatest stress in his 

 conclusions upon the paleobotanic evidence, because it is 

 this knowledge that he and his associates at Washington 



^ Bull. Geol. Soc. America, 30, 499-565, 1919. 



