206 GLACIAL FORMATIONS OF ERIE AND OHIO BASINS. 



shorter than that of some of the higher outlets, but it carried a much greater 

 volume of water. The next stage marks the close of the Genesee Lake as a 

 local body of water. It then became merged with the great body known as 

 Lake Warren, and discharged westward to the Mississippi. At the Lake 

 Warren and later stages definite beaches were formed, which are considered 

 in Chapter XVI. 



MORAINAL LAKES. 



Passing over minor pondings of the river occurring as a result of 

 irregularities in the drift filling, only the three most conspicuous cases of 

 damming are considered; one of these is at Portageville, another at Mount 

 Morris, and the third above Rochester. These have all received the 

 attention of Fairchild,^ whose descriptions are here given: 



At Portageville the bi"oad, deep valley was completely dammed with drift, and 

 the river found its outlet over the east rock wall of the buried valley. After cutting 

 through perhaps 75 feet of drift the river had to cut through about 125 feet of 

 Portage shales before the lake was drained. This probably required a length of 

 time comparable to the life of one of the stages of glacial waters. 



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

 that all the numerous and strong terraces found in the valle}' 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 bj'^ 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 

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

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



The St. Helena moi'ainal lake, which existed in the postglacial part of the 

 Genesee Valley above Mount Morris, has 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 rtiorainal 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 "rapids." This lake could not 

 have been over 560 feet in altitude, the height of the drumloid barrier on the east, 

 and Avas probablj^ only 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 verj^ 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. 



1 Bull. Geol. Soc. America, Vol. VII, pp. 449-450. 



