332 ELIOT BLACKW ELDER 



the zone of loess deposition, and are now so much weathered 

 that the large feldspar crystals protrude and some of them can be 

 picked out with the fingers. The coarse, unassorted, and unstrati- 

 fied character of these deposits suggests that they may be glacial; 

 and their isolated situation indicates that they have suffered greatly 

 from erosion. They are tentatively referred to the Buffalo drift. 



Glacial scratches are of course found only on bowlders of resist- 

 ant rock and even then only where they have been effectually 

 insulated from the action of the weather. Striated bowlders of 

 Buffalo age were found in considerable numbers in the new railroad 

 cuts, southeast of Ashton, Idaho. In that locality the old drift is 

 more or less cemented by lime carbonate. 



From these facts it seems certain that the changes which have 

 taken place since the deposition of these bodies of till are very much 

 greater than those which occurred between the making of the Bull 

 Lake and Pinedale series of moraines. The conditions imply that 

 the period between the Buffalo and the Bull Lake glacial stages 

 was several times as long as the next succeeding interglacial inter- 

 val, and many times longer than the post-glacial epoch. 



Glacial drift comparable to the Buffalo moraine in its relations 

 seems to cover most of the plateau of Yellowstone Park. Even 

 in the seventies, as a member of the Hayden Survey, Holmes^ 

 recognized the fact that the deep gorge of the Yellowstone must 

 have been cut after the deposition of the glacial drift which mantles 

 the surrounding plateau. For some unaccountable reason, this 

 early recognition of drift much older than the fresh moraines in the 

 Rocky Mountain region seems to have remained unnoticed and is 

 not mentioned even in more recent comprehensive papers on the 

 geology of Yellowstone Park itself. 



Although its full extent is no longer traceable, it is evident 

 that the Buffalo ice covered a much larger area than the glaciers 

 of the Bull Lake and Pinedale epoch. The latter were valley 

 glaciers, which in but few instances pushed beyond the mouths of 

 the canyons in which they developed. The Buffalo ice of the Teton 

 back-slope, and probably also of Yellowstone Park, spread far 



^ W. H. Holmes, "Glacial Phenomena in the Yellowstone Park," Am. Naturalist, 

 XV (iSSi), 203-8. 



