RELATION OF PROBOSCIDEAN REMAINS TO NEBRASKAN GUMBOTIL 83 



to the till with which they are associated. If these gravels were deposited in 

 front of an advancing ice-sheet and on a surface on which mammals were 

 living, the gravels and their included fossil remains might later be plowed up 

 by the ice-sheet and become incorporated in the drift with which the gravels 

 are now associated. The evidence of the age and the habitat of proboscideans 

 gained from the discovery near Osceola would seem to strengthen rather than 

 weaken this intei'pretation. Moreover, it may be inferred, perhaps, that re- 

 mains of mammals and other animals will be detected more rarely in till than 

 in gravels, since the crumbly fossil bones which are imbedded in till are de- 

 stroyed readily when a cutting is being made by a steam shovel or other ma- 

 chinery, whereas when the bones are in gravels they are likely to be silicifled 

 and therefore less likely to be destroyed, and hence more frequently detected. 



Discussion 



Dr. James H. Lees : I have recently examined a proboscidean tusk found at 

 Des Moines buried in loess of Peorian age which lies on wind-blown sand over- 

 lying Kansan till. The animal evidently was living on the Kansan plain while 

 the loess was being deposited — that is, later than the recession of the lowan 

 glacier. This occurrence, with that described by Doctor Kay as well as others, 

 over Iowa and elsewhere, shows the range of proboscideans through a great 

 part of Pleistocene time. 



VOTE OF THANKS 



A hearty vote of thanks to the Department of Geology of the Univer- 

 sity of Chicago^ the local committee, and in particular to Prof. R. T. 

 Chamberlin, was passed, in recognition of hospitalities extended and 

 facilities supplied, making the Chicago meeting one of the most success- 

 ful in the history of the Society. 



PRELIMINARY SKETCH OF THE HISTORY OF THE LOWER 3IISS0URI ^ 

 BY FRANK C. GREENE 



{Read before the Society December 30, 1920) 



CONTENTS 



Page 



Introduction 83 



Preglaclal Platte Valley 84 



Preglacial Kansas Valley 85 



Glacial and postglacial changes 86 



Introduction 



The following brief notes must be considered as far from complete, but it is 

 believed that they are of sufficient interest to justify their presentation. They 

 are the result of five years' observations made in connection with other work 



^ Manuscript received by the Secretary of the Society November 9, 1920. 



