362 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 1917. 



well-marked events which occurred simultaneously over at least the 

 whole of northern Europe. The proof that the simultaneity ex- 

 tended also to the glacial periods of other continents is naturally more 

 difficult, since direct correlation is mostly out of the question. A 

 great deal of evidence on the subject, based chiefly on the amount 

 of weathering undergone, has been brought forward by F, Lcverett 

 (131). After personally examining a great number of exposures in 

 America and the most typical ones in Europe, he was convinced 

 that the four great periods into which the American glacial deposits 

 fall show such remarkable resemblances with the periods in Europe, 

 both in the amount of weathering undergone and in the intervals 

 between the glaciations, that the two series must be directly com- 

 parable. These stages are: 



1 A review of the evidences of the lowan stage of glaciation was made in 1914 and 

 1915 by W. C. Aldcn and Morris M. Leighton for the United States and Iowa Geological 

 Surveys. As stated in their report, which is published in volume 26 of the Iowa Geo- 

 logical Survey, these gentlemen reached the conclusion " that there is what seems to the 

 writers to be good evidence of the presence of a post-Kansan drift sheet in northeast 

 Iowa and that this drift appears to be older than the Wisconsin and younger than the 

 Illinoian drift * * * There is. therefore, warrant for the continued use of lowan 

 drift and lowan stage of glaciation as major subdivisions of the Pleistocene classifica- 

 tion." Following is the classification in use at present by the United States Geological 

 Survey : 



PLEISTOCENE EPOCH. 



9. Wisconsin stage of glaciation (of Chamberlin). 



8. Peorian stage of deglaciation (of Leverett). 

 7. lowan stage of glaciation (of Iowa geologists). 



6. Sangamon stage of deglaciation (of Leverett). 

 5. Illinoian stage of glaciation (of Leverett). 



4. Yarmouth stage of deglaciation (of Leverett). 

 3. Kansan stage of glaciation (of Iowa geologists). 



2. Aftonian stage of deglaciation (of Chamberlin). 

 1. Nebraskan stage of glaciation (of Iowa geologists) (pre-Kansan of Chamberlin) 



(Jerseyan of eastern United States). 



The evidence is entirely in favor of the exactness of the time agree- 

 ment except in the case of the Illinoian, which seems somewhat older 

 than the Riss; here he considers that the differences in the amount 

 of weathering are accounted for by the differences in the amount 

 of rainfall at present. 



Independent evidence for this simultaneity was given recently by 

 A. P. Coleman (132), who from the amount of erosion estimated the 



