WARREN AND IROQUOIS WATERS. 445 



Genesee region the al'ea is today comparatively smooth, except for recent 

 stream excavation and the drumloid ridges. 



A brief pause of the glacier front at the southern edge of Rochester had 

 accumulated an east-and-west crescentic kame-moraine. * which after the 

 withdrawal of the Warren waters probably acted as a low barrier in the 

 course of the river and caused a shallow morainal lake (see page 450). 

 As the waters fell the river extended its channel over the abandoned lake 

 beds. From Mount Morris to below Avon it meandered over the silted 

 floor of its old valley. Beyond Avon the ancient valley is lost, and the 

 river wandered northward among the drumloid ridges for 10 miles and 

 then took a more direct course, east of north. In the cut through the 

 moraine the river is now on rock, and this point, locally known as the 

 " rapids," is the extreme head of the Rochester canyon of the Genesee; 

 but the excavation of the gorge did not begin in earnest until the next, 

 or Iroquois stage. 



The Warren stage ended only when the ice-dam by its melting opened 

 up an outlet channel in the Mohawk valley lower than the Chicago 

 channel. The waters then fell, how gradually we do not yet know, to 

 the level of the '' Ridge road." at Rochester, and the next and last stage 

 of the glacial waters was inaugurated. 



NINTH ST A GE : IROQ UOIS WA TERS. 



Outlet by Rome to the Mohawk and the Hudson. 



To glacial geologists the characters in general of lake Iroquois are too 

 well known to need description here. A strong beach, locally known as 

 the •' Ridge road," extends east and west across westeri>New York with 

 an altitude across Monroe county of 430 to 440 feet. During this episode 

 the Genesee river debouched into lake Iroquois at what is now the north- 

 ern edge of the city of Rochester and spread out a broad subaqueous 

 delta of silt. This delta is seen more clearly upon the eastern side of the 

 river, extending northward to lake Ontario and eastward to Irondequiot 

 bay, being deeply scored by recent drainage. Numerous boulders and 

 other evidence of ice-rafting occur, and cuttings in the clay reveal con- 

 tortions due to crushing or pushing of the beds, evidently produced by 

 readvance of the ice or by the dragging of icebergs (see plate 21, figure 2). 



The Genesee canyon at Rochester was begun during the Iroquois stage. 

 South of the Pinnacle moraine the Genesee waters were ponded for a time 

 in a shallow morainal lake. North of the morainic dam, at the " rapids," 

 the river was a swift stream with rock channel and broke over the edge 

 of the Niagara limestone at some undetermined point north of the present 



*The Kame-Moraine at Rochester, N. Y. H. L. Fairchild. American Geologist, vol. xvi, pp. 

 39-51, 1895. 



