GLACIAL GEOLOGY OF THE SARATOGA QUADRANGLE 33 



Fig. 4 Diagrams illustrating the development of the Adirondack-Hudson 

 valley. Diagram no. 1 shows the contour in cross-section of the preglacial 

 intermountain depression, in the locality of Spiers Falls. No. 2 shows the 

 condition at the beginning of the interglacial epoch; the floor of the depres- 

 sion is covered with till produced by the earlier glaciation. No. 3 shows 

 the condition at the end of the interglacial epoch; the till has been swept 

 away from the floor of the valley and a channel cut into the rocks by the 

 interglacial river. No. 4 shows conditions after the last retreat of the 

 ice sheet, or end of the Wisconsin stage. The walls of the channel and 

 the slopes have been worn down by the ice erosion of the last glacial epoch 

 and the valley has been filled with till left at the final withdrawal of the 

 ice. No. 5 shows present conditions. In postglacial times the river has 

 swept away most of the till from the floor and slopes of the valley and has 

 cut (at Spiers Falls) a channel in bedrock. 



