THE 



^ OCT - 3 1921 ^ 



AMERICAN JOURNAL OF STTENCE 



[FIFTH SERIES.] 



Aet. Xiy. — Further Remarhs on the Evolution of 

 Geologic Climates ; by F. H. Knowlton.^ 



In the April, 1921 number of this Journal there are 

 two articles critical of my recent paper on ^^ Evolution 

 of Geologic Climates.'^ These are: ^'Paleobotany and 

 the earth ^s early history," by A. P. Coleman, and ''Evo- 

 lution of geologic climates," by Charles Schuchert. 

 These articles seem to call for brief consideration. 



The thesis of my paper (p. 501) reads in part as 

 follows : 



"Relative uniformity, mildness, and comparative equability of 

 climate, accompanied by high humidity, 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 

 condition. ' ' 



That the truth of this statement is very generally 

 recognized is shown even by the admission of both Pro- 

 fessor Coleman and Professor Schuchert. Thus the 

 former says: 



"His [Knowlton's] account of the vegetation of the past con- 

 firms and heightens the impression left by paleozoology that 

 during the greater part of the world's history temperatures have 

 been genial even in the far north and far south where frigid 

 climates now reign. ' ' 



And Schuchert says : 



"Any paleontologist who is familiar with the climatic aspects 



^ Published with the permission of the Director of the U. S. Geological 

 Survey. 



Am. Joue. Sci. — Fifth Series, Vol. II, No. 10. — October, 1921. 

 13 



