8o NEW YORK STATE MUSEUM 



postlacustrine deformation and tilting; a subject treated more in 

 detail on a later page. 



The outlet of the Wilmington lake was through the gulf and hence 

 southeast to cross and then south to near Elizabethtown. The escap- 

 ing waters were forced to take such a course because of the ice lying 

 in the valley of the East branch of the Ausable with its southern 

 wall at Lower Jay. Another body of ice blocked the narrow valley 

 now occupied by Trout pond. 



The gulf channel contains a number of Pleistocene cataracts of 

 which the remarkably beautiful Copperas pond is the most striking 

 example. 



Upper phase of Upper Jay lake. The Upper Jay lake, like its 

 predecessor, the Wilmington lake, has left terraces and beaches 

 that are very definite in character. One beach on the hill a mile 

 north of Keene is loi 7.7 feet in altitude while still another in the 

 Ausable sheet is 1045 ^eet above tide. The controlling spillway is 

 situated i^ miles north of Bald mountain. The part of the lake that 

 existed in the Mount Marcy area was only 2 miles long. 



Lower phase of the Upper Jay lake. A lower phase of the Upper 

 Jay lake is indicated by beaches and terraces in the Lake Placid sheet 

 at 994 feet, and was almost entirely confined to the Lake Placid and 

 Ausable quadrangles. 



The lakes that succeeded the Upper Jay lakes do not concern us 

 as they did not occupy any portion of the Mount Marcy quadrangle. 

 Yet for an understanding of the postlacustrine deformation the well- 

 established levels are here listed, with their altitudes : Haselton lake, 

 967 feet ; Lower Jay lake, 930 feet ; Otis lake, 903 feet ; Rocky 

 Branch lake, 860 feet ; " Clififord " lake, 835 feet ; " Marine level," 

 646 feet. 



Postlacustrine Deformation and Tilting^ 



It has been pointed out that at the maximum extent of the conti- 

 nental ice sheet the load upon the land surface must have been tre- 

 mendous and must have subjected the land to great compressional 

 stress, which caused it to be depressed below its former level. Since 

 the ice was thicker in the north than in the south the amount of 

 deformation was greater in the northern part of the State. 



With the removal of the load by the melting of the ice the land 

 has " sprung " back, thus elevating the surface and tilting the shore 



1 This subject of deformation has not yet been fully considered by structural 

 geologists in the light of isostasy. 



