26 PLEISTOCENE OF INDIANA AND MICHIGAN. 



It is an open question whether the oldest drift is represented in the southern peninsula 

 of Michigan and in Indiana, the area covered by the present report. The presence of copper 

 nuggets in the drift over the entire southern peninsula and southeastward into central Ohio 

 seems to call for an ice movement from the Lake Superior region across the southern peninsula 

 and probably through the Huron basin to the limits reached by the nuggets. The ice move- 

 ment in the IUinoian and Wisconsin stages of glaciation seems to have been such that copper 

 could not have been carried into Ohio from the Lake Superior region. It appears, therefore, 

 that this transportation was effected in Kansan time or earlier, at a time when the Labrador 

 glaciation was relatively weak. 



FIRST OR AFTONIAN INTERGLACIAL STAGE. 



Evidence of the Aftonian interglacial stage is clearest in the region west of the Mississippi. 

 It was noted about 1888 by Chamberlin and McGee near Afton, Iowa, and was made by Chain- 

 berlin 1 the type locality for the interval. Bain 2 subsequently brought out additional data 

 concerning it. Calvin 3 and Shimek i have recently presented results of studies in western 

 Iowa which give a clearer understanding of this deglaciation interval and which make it 

 appear that a warm temperate fauna had possession of that region between the pre-Kansan 

 and Kansan stages of glaciation. 



KANSAN DRIFT. 



The Kansan drift, which in the Mississippi Valley overlies the pre- Kansan drift and which 

 is. thought to extend beyond its limits in Kansas and Missouri, was first clearly brought to 

 notice in its proper relations by Calvin and his associates on the Iowa Geological Survey and 

 is discussed in the several volumes of that survey which deal with counties of eastern, southern, 

 and western Iowa. It is an open question whether this drift is represented in southern Michi- 

 gan and Indiana. Possibly the copper noted above was brought in at this instead of pre- 

 Kansan time. As a surface sheet the Kansan is displayed in the States west of the Mississippi, 

 though even there it is covered by loess. It is also overridden to some extent near the Mis- 

 sissippi by the Illinoian drift. 



SECOND OR YARMOUTH INTERGLACIAL STAGE. 

 SOIL A.ND WEATHERED ZONE. 



The first part of the second interglacial stage embraces a long interval, during which the 

 surface of the Kansan drift was weathered and the soil and peat beds which separate the Kansan 

 from the overlapping Illinoian drift were developed. The region of overlap is along the borders 

 of the Mississippi south of the driftless area, in southeastern Iowa and western Illinois. The 

 locality where evidence of this interval was first clearly recognized is at Yarmouth (near 

 Burlington), Iowa, where the overlap is by the drift of the Labrador ice field upon that of 

 the Keewatin ice field. 



LOESS. 



Between the Yarmouth interglacial soil and weathered drift and the overlying Illinoian 

 drift, and therefore of pre-Illinoian age, there lies in places a deposit of loess, which is best 

 displayed in the region of overlap of the Illinoian on the Kansan drift, and which seems to 

 have resulted from a less humid climate than that under which the peat was formed. 



ILLINOIAN AND IOWAN DRIFTS. 



The IUinoian appears to be the most extensive drift sheet of the Labrador ice field. It 

 is thought to extend to the glacial boundary in Indiana as well as in neighboring parts of Olho, 

 Kentucky, and Illinois. The name Illinoian is applied because of the wide exposure of this 



1 Classification of American glacial deposits: Jour. Geology, vol. 3, 1S95, p. 272. 



2 Bain, H. F., Proc. Iowa Acad. Sci., vol. 5, 1898, pp. 80-101. 



'Calvin, Samuel, Proc. Davenport Acad. Sci., vol. 10, 1907, pp. 18-31, 7 pis.; Bull. Geol. Soc. America, vol. 20, 1909, pp. 136-139, 341-356. 

 4 Shimek, Bohumil, Bull. Geol. Soc. America, vol. 20, 1909, pp. 399-108, Pis. XXX-XXXVII; vol. 21, 1910, pp. 119-U0. 



