10 NEW YORK STATE MUSEUM 



channels were carved directly at the ice edge, or in other words 

 that the streams here laved the ice front. On the other hand the 

 Fairport-Lyons channel although initiated at the ice front con- 

 tinued to remain effective long after the ice had left that parallel, 

 for the reason that higher ground lies on the north. 



The higher (southward) and more interrupted channels lie on the 

 steeper part of the north-facing slope, formed by the scarp of the 

 Onondaga limestone, and are frequently only benches in the slope. 

 That is to say, only the south banks of the channels are in existence, 

 as the north bank was the glacier ice. The lower and more contin- 

 uous channels are in the soft Salina shales; those at Mumford, 

 Scottsville. Rush and Mendon [pi. 2] and Victor [pi. 3] being in the 

 upper and harder shales, while the channels east of the Cayuga 

 meridian are in the very soft and erodible lower (Vernon) shales. 



The maps will show that the stream flow was interrupted by 

 north and south depressions, and it will be understood that these 

 surfaces below the channels must have been occupied by standing 

 waters or lakes. Into these lakes the inflowing streams carried 

 their burdens of detritus and built deltas in the western margins of 

 the lakes. A necessity for the continuous flow was a sequence of 

 declining channels to the eastward. 



Two pronounced depressions lie athwart the general course of 

 the stream flow. One is the Genesee valley, some 3 to 4 miles wide, 

 in the waters of which the rivers from the west built broad deltas, 

 extending north from Fowlerville to Scottsville. The other depres- 

 sion is the Cayuga basin, the broad tract of the Montezuma marshes. 

 Over this stretch of about 25 miles, or between the meridians of 

 Geneva and Jordan the waters seem to have formed an extensive 

 but shallow lake. 



The eastern channels, in the Syracuse district and eastward, are 

 more broken by deep, narrow valleys. The plateau of southern 

 Xew York, trenched by pregiacial stream valleys, reaches to the 

 Syracuse parallel where it drops off abruptly. At different times 

 and for many centuries the glacier front rested against the steep 

 north edge of the plateau all the way from the Skaneateles meridian 

 east to Utica. and the escaping waters were forced to cut deep 

 trenches or notches in the north ends of the intervalley ridges. The 

 valleys in which waters were ponded with changing levels are: 

 Skaneateles, Otisco (Marcellus). Onondaga, Butternut and Lime- 

 stone, and several valleys farther east; all of which have been 

 described, in this relation, in former papers [see titles 25, 26. 28, 31]. 



