ANCIENT WATER LEVELS OP CHAMPLAIN-HUDSON VALLEYS 161j 



standing water. Between the lowest of this group of frontal 

 deposits on the north and ,the higher ones there intervenes the 

 remarkable " flat rock " areas or spillways of Altona extending 

 into the region northwestward as far as the internationial boun- 

 dary at Covey hill, Canada. 



Flat Rock spillioays [see pi. 18]. These bared surfaces of the 

 Potsdam sandstone mark the path of a torrential discharge of 

 water held on the northern slope of the mountains along a line 

 from the notch at '' the Gulf " [see pi. 25] on the international 

 boundary line to a point wesit of the village of West Ghazy, a dis- 

 tance of about 19 miles. It is necessary to suppose that the ice 

 front lay along the lower side of this spillway belt, which thus 

 becomes quite as definite as a frontal moraine in the fixation 

 of the position of the ice at this time. This line of evidence is 

 confirmed by the occurrence of strong frontal deposits along the 

 lower margin of the spillway zone near West Chazy at " Cobble- 

 stone hill " and northward [see geologic map of the Mooers quad- 

 rangle, pi. 29] . 



More important than all this is the evidence afforded by the 

 torrential action concerning the hight of the standing water 

 then in the valley of Lake Champlain. The lower margin of the 

 stripped bed rock near West Chazy descends nearly to the 620 

 foot contour line; its upper limit in the district is approximately 

 900 feet; farther north its upper limit is as high as 910^ feet, and 

 in the Gulf there is a water pool [see pi. 19] at the base of an 

 abandoned waterfall at 810^ feet, and there isi a lower lakelet in 

 a chasm at 645^ feet [see pi. 20]. These lakelets would not have 

 been produced by a fall of water into this channel when it was 

 deeply submerged. There are evidences of water standing at 

 some episode in this phase east of the Gulf^ at a level between 



^ These elevations are from Mr Gilbert's notes, but have been taken inde- 

 pendently by myself. 



'^ There is a brief account of the Gulf given by Ebenezer Emmons in 

 the Geology of the Second District. [Clinton County, p. 309- 10, 1842 ] He 

 reports the small lake at the bottom as "said to be 350 feet deep." He also 

 states that "To account for the present condition of this rock, we have 

 therefore to gO' back to a period when some current swept through this 

 gorge with great force and power; for by no other means could the mate- 

 rials, which once filled the space between the present walls of the gulf, be 

 removed." This is the first notice I believe of this spillway in scientiflc 

 literature. 



