NEW FACTS AND REDISCUSSION 525 



below 360 feet in elevation or it may have resulted from recurring high- 

 water stages of the Mohawk waters. An overflow, once started, or, if 

 taking place recurrently at times of flooded waters, gradually through 

 erosion lowered the wall of the valley so that a permanent lateral outlet 

 stream was eventually established. The overflow waters from the Iro- 

 quois-Mohawk were engaged a longer time in cutting the Aqueduct gorge 

 than that at East Line because of the greater length of the former. The 

 fall or rapids of the overflow stream was first at Yischers Ferry, and it 

 was not until this fall had receded to Aqueduct, a distance of 5 miles, 

 that the full volume of the Mohawk waters was diverted to its present 

 channel. 



The explanation given by Fairchild of the origin of the Mohawk gorge 

 from Aqueduct eastward, namely, that it was due to a reversal in direc- 

 tion of the Iroquois-Mohawk currents in the Ballston Channel consequent 

 upon northward uplift of the region, while consonant with the steps of 

 glacial drainage history, as above set forth, seems to the writer improb- 

 able, as being out of accord with physical principles. It would seem that 

 regional uplift, taking into account the time element, would have in- 

 creased the erosional work of the stream, thus enabling it to deepen its 

 bed and to maintain its course, rather than have caused a reversal in the 

 direction of flow of its flooded waters. 



Deduction bearing on the Pleistocene History of the Champlain- 



Hudson Valley 



The erosional history of the lower Mohawk-middle Hudson region, as 

 above interpreted, is incompatible with the view that sealevel waters occu- 

 pied the Champlain-Hudson Valley in late Pleistocene times. The waters 

 which covered the region following the retreat of the ice-front, whether 

 forming a glacial lake or an estuary entering the Hudson Valley at New 

 York, had withdrawn from this territory while yet the outlet of the great 

 interior lakes was through the Mohawk Valley. The Saint Lawrence 

 Valley was still filled with ice and the front of the ice-sheet stood across 

 the Champlain-Hudson Valley somewhere north of the area described in 

 this paper. When the ice-front had so far retreated to the north as to 

 open a lower outlet along the northward slope of the Adirondacks, thus 

 ending the Iroquois-Mohawk stage of drainage, the new outlet may have 

 followed the Champlain-Hudson Valley to the ocean at New York. But 

 these waters, as they coursed through the middle Hudson region, were 

 certainly fluviatile, covering only the present valley bottom of the Hud- 



