I894-J 367 [Grabau. 
the Caneseraga, as well as across the northern end of tlie northern 
half of the valley of the Genesee, which had become separated 
fioni the southern half by the drift deposits at Portage and at 
Castile. A barrier near Rochester nine hundred feet or more in 
height would convert these valleys into lakes, the former extend- 
ing back to Dansville and beyond, while the latter would reach 
south as far as Castile. The barrier formed by the "Portage 
Ridge" would likewise transform the Genesee Valley south of 
Portageville into a lake extending nearly back to its source. 
There would thus be three additional "Finger Lakes," each 
having an altitude of about 1,300 feet A. T. That these condi- 
tions actually existed is shown by the character of the valley- 
bottoms and by the subsequent history of the Genesee. Between 
the Genesee Lake on the south and the Wyoming Lake on the 
north, there existed a small lake occupying the Glen Iris Valley. 
This lakelet received the drainage from the Genesee Lake which 
overflowed at the point on the left bank where the short gorge 
commences which to-day connects the valley on the south with 
Glen Iris. This course was necessitated by the height of the drift 
deposits on either side, there being at this point a slight depres- 
sion between them. Owing to the height of the drift hills which 
separated Glen Iris Lake from Wyoming Lake, no connection 
was established in this direction ; but the surplus water, over- 
flowing at the lowest point, took a course diagonally across the 
rocky plateau separating the two ancient valleys and entered the 
Caneseraga Lake at Mt. Morris. Thus commenced the wearing 
of that immense gorge which to-day extends from near the middle 
falls at Portage to Mt. Morris, with a total length of probably 
thirty miles, taking into account its sinuosity. As Glen Iris Lake 
was lowered by the deepening of this gorge a fall came into exist- 
ence over the side of the valley, at the mouth of the short gorge 
carrying in the water from Genesee Lake. This f:dl has receded 
comparatively little since that time, being to-day under the rail- 
road bridge which spans this gorge at its junction with Glen Iris 
Valley. The drainage of Genesee Lake was slow enough to 
admit of beach formations along its sides. On the final recession 
of the ice-sheet, the Caneseraga and Wyoming Lakes were 
lowered to near the level of the modern Genesee, the remainder 
being filled up. The Genesee was now the occupant of the 
northern half of the channel of the ancient Caneseraoa which was 
