THE IOWAN ICE INVASION" 345 



3. The Iowan drift is not a phase of the Kansan. 



4. The Iowan drift has certain very intimate relations to certain bodies of loess. 



5. The Iowan drift has no close relation to the Illinoian. 



Alden 6 affirms the existence of the Iowan drift in northeastern Iowa, coro- 

 borating Calvin's opinion, and remarks that "It is older than the Wisconsin 

 and seems to be distinctly younger than the Illinoian" (p. 119). Recently, 

 Alden and Leighton Ba have made a very careful and extensive study of the 

 Iowan drift, from which "the conclusion has been reached that there is what 

 seems to the writers to be good evidence of the presence of a post-Kansan drift 

 sheet in northeastern Iowa and that this drift appears to be older than the 

 Wisconsin and younger than the Illinoian drift. The writers are, therefore, in 

 the main in agreement with the late State Geologist, Dr. Samuel Calvin, in re- 

 gard to the Iowan drift. There is, therfore, warrant for continued use of 

 Iowan drift and Iowan stage of glaciation as major subdivisions of the Pleisto- 

 cene classification" (p. 56). 



II. The Peorian Interglacial Interval 



The interval between the Iowan and early Wisconsin drifts has been named 

 the Peorian by Leverett, 7 who says : "Extensive deposits of muck and peat at the 

 base of the Wisconsin drift in northern Illinois, notably in McHenry, Kane, 

 Dekalb, LaSalle, and Bureau counties, are in all probability immediately 

 underlain, in some cases at least, by Iowan drift. In central and eastern Illi- 

 nois the soil is in places underlain by a fossiliferous silt, referred with some con- 

 fidence to the Iowan loess. In eastern Illinois, as noted above the Iowan till 

 may be present. " Leverett's type locality, near Peoria, is unfortunate because 

 the loess here referred to the Iowan is possibly post-Illinoian and therefore 

 equivalent to the Sangamon interval. Some of these deposits may include 

 both the Illinoian and Iowan loesses, and old soils between these loesses may 

 be equivalent to the Peorian interval. 



The occurrence of Iowan drift in Illinois has been questioned, the fresh 

 till thot by Leverett and Hershey to be Iowan being ascribed to later erosion. 

 Alden says: 8 "It is quite possible, if not probable, that this till is underlain in 

 part at least by older drift, but that question is not here under discussion. 

 So far as the writer has observed there is no good ground for differentiating 

 the drift exposed at the surface into deposits of more than one stage of glaciation. 

 No intercalated, weathered zones, vegetal or other fossiliferous deposits are 

 known to separate one part of this drift from another. Such as have been 



•Bull. Geol. Soc. Amer., XXVII, pp. 117-119. 



«* Ann. Rep. Geol. Survey Iowa, XXVI, pp. 49-212, 1917. 



7 Illinois Glacial Lobe, p. 185. 



■ Alden, Joum. Geol., XVII, p. 696, 1909. 



