26 Smithsonian Exploration in Alaska in 1904 



The fragmental condition and scattered positions of these remains 

 places them in the category of secondary depositions. The state 

 of preservation of bones from these situations indicate they have not 

 been carried far. Generally they are unbroken (pi. 11, fig. 2). 



2. SEARCH FOR SKELETONS SHOULD BE MADE ON LAKE SHORES 



That the fluvio-glacial Pleistocene lakes of Alaska were subject 

 to annual winter freezing, at least at various stages of their ex- 

 istence, there appears no doubt, because scattered apparently in- 

 discriminately through the clays at varying depths and considera- 

 ble distances from the former shore lines of these basins are some 

 mammal remains. Their positions can only be accounted for by 

 supposing they were carried out on the waters of the lakes from the 

 adjacent shores or tributary streams by ice during spring breakups 

 and freshets, there to be dropped by its melting to their present 

 positions interbedded in the silts. There appears no other logical 

 way of explaining the presence of these bones in the lacustrine 

 areas. While their presence under these circumstances points to- 

 wards the lakes freezing over in winter we do not wish it under- 

 stood by this that Alaska then had winters as severe as those of 

 the present time, or that it was ice bound for the greater part of each 

 year, but that conditions were more nearly as they are in temperate 

 regions today. The main point is that the remains occur in the silts 

 as scattered depositions. The animals from which they are derived 

 probably died about the shores of these lakes and it is these Pleisto- 

 cene lake shores we must examine carefully if we are to obtain any- 

 thing like complete remains of the mammals inhabiting the region 

 at that time. 



VI. Pliocene in Alaska 



I. DEPOSITS. probable CHANGES OF LEVEL 



No extensive developments of Pliocene have been identified in 

 Alaska. Whether Pliocene time was mostly one of denudation 

 over this great area, ending with a subsidence accompanied by 

 changes in relief forming barriers across the main drainage courses 

 of the country, which in some cases appear to have been augmented 

 by flows of eruptives, remains to be shown. At any rate there 

 were barriers that localized the retention and deposition of the 

 Pleistocene lacustrine silts and clays throughout the drainage basins 

 in the majority of cases. In other instances the coarser silts along 

 valleys appear to have formed by a clogging of the channels by 



