﻿4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 59 



the various glacial sheets. In preparing this he has made use of 

 the maps in Leverett's Monographs 28 and 41 of the U. S. Geologi- 

 cal Survey, and of a map in the office of Dr. W. C. Alden, of the 

 Survey, on which map is shown the distribution of the drift of 

 different stages in the region west of that considered by Leverett in 

 the works mentioned. On the maps here shown the various drift- 

 sheets are mapped as accurately as is possible on a scale so small. 

 The drift-sheet most important for our purpose is the Wisconsin. 

 This sheet covers more or less completely Labrador, Nova Scotia, 

 and New England ; while farther west it extends southward to 

 a line running through Pennsylvania, a part of New York, Ohio, 

 and Indiana. Near the center of Illinois the line turns northward 

 into Wisconsin, where it passes to the east and north of a driftless 

 region. A great lobe of the sheet descends in Iowa to Des Moines, 

 and in eastern South Dakota is seen a smaller lobe. Thence the 

 southern border of the sheet continues westward to the Pacific 

 coast in Washington. 



In Ohio and Illinois the Illinoian drift-sheet extends southward 

 beyond the edge of the overlying Wisconsin. In northeastern Iowa 

 and the adjoining part of Minnesota is found the exposed part of 

 the Iowan sheet. West of the Mississippi River the Kansan sheet 

 extends southward beyond the Wisconsin, and a fringe of it is seen 

 along the western border of the driftless region of Wisconsin and 

 Iowa. The Nebraskan drift-sheet is wholly covered by the later 

 ones and is not shown. The various drift-sheets are theoretically 

 separated more or less completely by interglacial deposits. It may 

 be convenient to have the order shown here in which the glacial and 

 interglacial stages succeeded one another. The interglacial stages 



are italicized. TT7 . 



9. Wisconsin. 



8. Peorian. 



7. Iowan. 



6. Sangamon. 



5. Illinoian. 



4. Yarmouth. 



3. Kansan. 



2. Aftonian. 



1. Nebraskan. 

 On these maps it is proposed to indicate where remains of various 

 Pleistocene mammals have been discovered. The writer has en- 

 deavored to make a thorough examination of the literature on the 

 subject, and believes that very few mentions of discoveries of the 



