158 THE ICE AGE IN NORTH AMERICA. 



gheny might seem to be more appropriate to the chapter on 

 Glacial Dams, Lakes, and Waterfalls, but it is so intimately 

 related to the facts connected with the extreme extension of 

 the continental glacier in the Appalachian region that we 

 introduce it here, expecting the reader to refer to it again for 

 facts which have an important bearing on later theoretical 

 discussions. In itself, however, it is one of the most interesting 

 problems ever presented to the geographer and the geolo- 

 gist: I am permitted to quote freely from the unpublished 

 report of Professor E. H. Williams upon the subject, and to 

 make use of his extensive collection of facts. 



LAKE ALLEGHENY. 



Professor Williams writes, ' 'Kansan' drift throughout 

 Pennsylvania is characterized by native copper. I have a 

 piece from Warren (40 feet below the surface), and farmers 

 have come to me at Bethlehem to come and see their 'cop- 

 per mine/ Mr. Albert G. Rau, Dean of the Moravian Col- 

 lege has, at numerous points, picked up rolled fragments 

 from 'Kansan' gravels. This seems to point to a Lake Su- 

 perior passage by the ice — hence the glacier which first in- 

 vaded this part of the state came from the northwest, and 

 therefore moved against the drainage and presented so effect- 

 ual a dam that, with the exception of the hilltops, north- 

 western Pennsylvania and adjacent New York were sub- 

 merged by a lake whose eastern shores in Pennsylvania were 

 the highlands of Potter County and their extension south- 

 ward, while McKean County extended into it like a broad 

 promontory deeply gashed by its river systems. The name 

 Allegheny is proposed for this lake which originated long be- 

 fore the advent of glacial ice to the immediate region and 

 which, being but slightly drained subglacially, sent its wa- 

 ters southwards over the cols into other drainage systems. 

 As the glacier advanced it constricted the area of escape and 

 when it reached the line of the present Allegheny it formed, 



