ANCIENT WATER LEVELS OF CH A MPLAIN— HUDSON VALLEYS 77 



when the Hudson gorge from Fort Edward south to Albany was 

 not so deeply excavated as it now is. 



Wood creek channel. The valley of Wood creek, to which 

 reference, will be repeatedly made in this report, forms at present 

 the lowest line of communication between the upper Hudson valley 

 and that of Lake Champlain. The divide between these two val- 

 leys lies at an elevation of about 147 feet, near Dunham basin [see 

 pl.13]. It will be noted from the map that the old gorge of the 

 Hudson appears to be continued in this direction and that the 

 Hudson river above Fort Edward falls into this broad open 

 channel along a new path characterized by falls and a much less 

 width. As will be noted in a later chapter the Wood creek 

 channel appears to have been for a time the outlet of a glacial 

 dammed lake extending from near Dunham basin northward over 

 the site of Lake Champlain. 



PHYSIOGRAPHY OF THE CHAMPLAIN- VALLEY 



Lake Champlain appears to occupy an irregular depression ex- 

 cavated mostly in the lower Silurian and Cambrian rocks corre- 

 sponding in this respect to the Hudson in its gorge from Albany 

 southward. The present depth of this erosion feature is at least 

 500 feet below sea level in the deeper part of the lake. The equiva- 

 lent of the rock terraces of the Hudson, or the floor of the older, 

 wider valley in which the newer and narrow channel has been ex- 

 cavated, is found along the shores of Lake Champlain in a dis- 

 sected rock surface as in Essex, along the Vermont shore south of 

 Burlington, and widely developed about the northern part of the 

 lake. This ancient valley floor is about 300 feet above the present 

 sea level. Both this surface and the newer valley excavated in it 

 have suffered more from glacial erosion than has the analogous 

 topography of the lower Hudson valley. The Wisconsin ice sheet 

 pressed into the northern portal of the Champlain valley in a 

 strong flowage coming from the northeast rather than from the 

 north so that the maximum erosion line must have been thrown 

 toward the base of the Adirondacks in the position of the lake 

 basin. No facts are at hand, however, to show how much, if any. 

 the lake basin was deepened by ice action. Many of the streams, 

 such as the Ausable, which now enter the lake over high level rock 



