1(>2 NEW YORK STATE MUSEUM 



the levels of the two lakelets. An ice barrier extending to the 

 north and west of Covey hill caused the waters along its front 

 to escape through the pass on the south side of the hill. When 

 that ice barrier withdrew from the northern sloi>e of the hill it 

 would liave at once allowed the waters to take a lower channel 

 around the northern slope of the hill and at the same time it would 

 have removed the baiTier Avhich on the east of the hill retained 

 the glacial lake at its high level. It can not be supposed there- 

 fore that any part of the Gulf was excavated after the ice sheet 

 withdrew from the northern side of Covey hill. The occurrence 

 of the high beaches on the northwest corner of the Mooers quad- 

 rangle at a level above the lower lake in the Gulf chasm, 

 together with the line of beaches along the northern border of 

 the Altona flat rocks^ — there lying above the lower limit of these 

 rocks — makes it reasonable to suppose that after the scouring 

 of the flat rock spillways had been well begun there was, at 

 least at the northern end of the Champlain valley, a local 

 relative rise of the water level as the ice receded and this would 

 be a consequence of the downsinking of the land in this northern 

 region. An uplift of the country about the lower Hudson would 

 have accomj)lished the same result. That there was a local change 

 of the first description is probable since as will be brought out 

 more fully later, the shore lines in the Chamx)lain district are 

 more steeply inclined to the south than are the earlier water levels 

 between New York and Albany. The reversed direction of tilt- 

 ing of the land to the south which has since taken place would 

 produce the observed discordance if the land were tilted more 

 and more to the north while the glacial lake advanced northward 

 in the face of the retreating ice sheet. 



Evidence from the northern face of Covey hill [see pi. 25]. As 

 is shown in more detail in ilie report on the Mooers quadrangle, 

 the northern face of Covey hill is a critical field for the study of 

 water levels in the upper St Lawrence valley. Mr Gilbert appears 

 to have been the first to perceive this point and was I believe the 

 first to make critical though unpublished observations on this 

 interesting locality. Covey hill and the Gulf are localities at 

 whirli most lines of evidence presented in this paper come to a 

 focus; hence the various features which are there presented will 

 be found often under sepai-ate headings in this report. 



