450 H. L. FAIRCHILD — GLACIAL GENESEE LAKES. 



This probably required a length of time comparable to the life of one of 

 the stages of glacial waters. 



The top of the rock-cat is about 1,250 feet, by estimate, and it seems 

 probable that all the numerous and strong terraces found in the valley 

 from Portage up to Caneadea and below about 1,275 feet altitude belong 

 to the morainal lake. At Portageville there are good terraces at 1,157 

 and 1,185 feet, and others, by aneroid, at 1,220, 1,255 and 1,265 feet. At 

 Rossburg are conspicuous plateaus, the lower ones possibly detrital river 

 plains, but higher ones at about 1,200 feet and over. At Fillmore the 

 terraces are 1,218, 1,233 and 1,252 feet, and at Houghton is a good ter- 

 race, estimated at about 1,250 feet. At Caneadea the terraces are well 

 developed and have altitudes of 1,243 and 1,273 feet. 



The Saint Helena morainal lake, Avhich existed in the postglacial part 

 of the Genesee valley above Mount Morris, lias not been studied. The 

 top of the rock-gorge, locally known as the " high banks," is not far over 

 900 feet. The cut, about 300 feet deep, is in dark Hamilton shales and 

 was made during the Warren and Iroquois stages. On account of the 

 narrowness of the valley and the steepness of the slopes, the water planes 

 of the morainal lake are not well preserved, but can undoubtedly be 

 found by searching. 



A shallow morainal lake probably existed southwest of Rochester, due 

 to the morainic dam which the river has cut through at the " ra})ids." 

 This lake could not have been over 560 feet in altitude, the height of the 

 drumloid barrier on the east, and was })robabl3^ onl}' 540 to 550 feet, the 

 present altitude of the moraine. It could therefore not have been deep, 

 but it extended up the valley several miles, and had a broad expanse east 

 and west, with very irregular form. For the brief episode of its existence 

 this lake received from the river a large amount of detritus, which was 

 deposited as a smooth floor, with an altitude of 525 feet, making the largest 

 level tract in the region of Rochester. 



IN TRIBUTARY STREAMS. 



Rock ravines w'ith steep sides, occurring in the course of Genesee 

 tributaries, indicate in all cases a diverting of the streams from their old 

 channels. The occurrence of such rock-cuts is given in a preceding sec- 

 tion of this paper (pages 427-429). The diversion of the drainage was 

 due to damming by drift, and it follows that such part of the valley above 

 the dam as was not filled with the drift must have been occupied with 

 ponded water up to at least the level of the top of the rock-cut. 



The writer has observed but few of the sites of these morainal lakes, 

 and these will be described very briefly. 



