156 THE ICE AGE IN NORTH AMERICA, 



All these facts became clear when it was known that the 

 ice crossed the Susquehanna and advanced to the summit of 

 the mountains lying between that river and the Juniata. The 

 glacial gravels at Lewistown came from a stream which poured 

 over the col at Adamsburg where the ice was arrested in its 

 movement. The bowldery deposits farther up the Juniata 

 near Huntingdon came from an immense glacial stream which 

 poured over the col between the head of Bald Eagle Creek and 

 a branch of the Juniata joining the main stream at Tyrone. 

 Bald Eagle Valley had been occupied by a long narrow glacial 

 lake occasioned by the obstruction of its mouth at Lock Haven, 

 where the depth of the water was 570 feet. The col above Ty- 

 rone has an elevation of 1,100 feet. The shore lines of this 

 temporary lake (which has appropriately been named Lake 

 Lesley) can easily be traced, and is marked by great cones of 

 gravel where tributary streams came in from the east. The 

 erratics thrown up to such a great height on the west side of 

 Warrior's Mountain are evidently due to high and tumultuous 

 water produced by an ice-gorge where the stream enters 

 the narrow channel across the mountain ridge. Numerous 

 evidences of the damming of the West Branch of the Sus- 

 quehanna are to be found as far up as Emporium on the 

 Sinnemahoning River. 



Northwestward from Lock Haven the border of the Kansan 

 drift is lost in the wildernesses of Lycoming and Potter 

 counties, becoming recognizable again near Coudersport, 

 beyond which it disappears under the moraine of Lewis and 

 Wright to reappear again on the highlands of Warren, Ve- 

 nango and Butler counties west of the Allegheny River where 

 the elevations rise above the flooded regions produced by the 

 ice-dams which reversed the drainage of the whole basin 

 west of the Alleghenies. A simple illustration shows the 

 probable overlapping of borders as suggested by Professor 

 Williams. 



The history of the reversal of the drainage of the Alle- 



