730 ABSTRACTS OF PAPERS 



(c) 17,000 square miles in the Yukon flats, (d) several thousand square 

 miles on the upper Yukon region in Canada and smaller areas. The domi- 

 nant material is outwash, and this extends long distances outside the country 

 actually glaciated. In places there is wind-blown loess associated with this. 

 In some localities it is still being deposited, and in the Copper River basin 

 it has been accumulating during the time required for the growth of six or 

 seven generations of trees. There is also some till, but this is largely buried 

 beneath outwash. Lake deix)sits, eskers, kames, and buried vegetation are 

 also found, but thus far no one has found drumlins. In thickness some of 

 these deposits rival those of the Middle West, one instance being known of 

 probably 800 feet of gravel, sand, etcetera, grading out from the mountains to 

 less than 100 feet fifty miles away. The presence or absence of these drift de- 

 posits seems to be chiefly a matter of favorable topography and existing de- 

 glaciation — a process much like that formerly in progress in northeastern and 

 central United States. 



Discussion 



Dr. C. A. Davis : The estimate of the age of the deposits shown in the 

 photographs, based on the age of the included stumps alone, is very conserva- 

 tive, since the stumps shown are thoroughly decayed. Such decay is usually 

 subaerial, and when once the stump is buried it practically ceases. If the 

 average age of the stumps shown in the strata were 150 years, 50 years 

 would probably be a fair estimate of the added time required to bury it 

 completely, so that at least 200 years is represented in each layer of stumps. 



Prof. W. M. Davis called attention to the large volume of peripheral de- 

 posits as indicating large erosion in mountain sources of glaciers ; still larger 

 when it is recognized that much glacially eroded material is not recognizable 

 in glacial deposits, but is washed far down the outflowing rivers and even to 

 the sea. 



PRE-WI8C0N8IN GLACIAL DRIFT IN THE REGION OF GLACIER PARK, 



MONTANA 



BY WILLIAM C. ALDEN 



Published as pages 687-708 of this volume. 



Discussion 



Prof. A. P. Coleman: At Calgary, 100 miles north of the region spoken of 

 by Mr. Alden, there are two or three sheets of boulder clay. One coming 

 from the mountains is lowest and is covered by interglacial material, followed 

 by a boulder clay containing Laureutian boulders which came from the Kee- 

 watin center. The lowest boulder clay nuist be nmch older than the Wisconsin 

 ice age. 



Prof. W. W. Atwood : Mr. Alden has been working in a region of unusual 

 interest from the standpoint of glacial geologj'. It is probable that he will 

 secure some other significant data. I should like to ask a few questions. 



Is it not possible that the Blackfoot peneplain, as described by Mr. Willis, 



