Gravels Underlying Pleistocene Silts 2'j 



the Pleistocene sediments where remnants of them remain today 

 hanging to the valley sides. Whether these changes belong to the 

 later Pliocene or early Pleistocene remains to be settled. 



VII. Gravels Underlying Pleistocene Silts 



Underlying the Pleistocene silts in some places are gravel beds 

 whose possible Pliocene age has been suggested by Spurr (Geol. 

 Yukon Gold District, i8th. Ann. Rep. U. S. Geol. Sur., Part 3. p. 

 199). But from the relation they bear to the silts in the Old Crow 

 Basin, where the gravel terrane forms a typical beach deposit con- 

 temporary with the lacustrine silts it appears they may be considered 

 of the same age. 



A'lII. Brief Outline of Pleistocene of Alaska 



I. MAP 



In order to show more clearly how these scattered and original 

 depositions of mammal remains occur, a sketch of the nature, dis- 

 tribution, and extent, of the Pleistocene, with such reference to the 

 Recent as concerns the Mammoth will be attempted. 



Through the kindness of Mr. Alfred H. Brooks, Geologist in 

 charge of the U. S. Geological Survey work in Alaska, the writer 

 is enabled to present a map of Alaska showing the latest results 

 of the field observations of members of that survey as regards the 

 Quaternary. This map (pi. iii) shows the boundary between the 

 southeastern glaciated and the northwestern non-glaciated areas 

 within Alaska, together with the distribution of the unconsolidated 

 sediments forming the Pleistocene and Recent. However, this 

 limit while practically a continuous line must not be interpreted as 

 the limit of a continuous ice-sheet, but of individual glaciers. The 

 areas occupied by the " Yukon Silts " and " Kowak Clays " are dif- 

 ferentiated in a general way as far as known. These silts and 

 clays have special significance and are no doubt more numerous and 

 extensive than here shown. 



2. STRATIGRAPHIC RELATIONS OF PLEISTOCENE 



The fluvial and lacustrine beds of Alaska and the adjacent un- 

 glaciated portion of Canada represent the whole Pleistocene period. 

 The silts with their occasional gravels rest unconformably on the 

 eroded surfaces of the older formations. They appear most con- 

 spicuously as terraces along the sides of the valleys. Where the 



