202 GLACIAL FORMATIONS OF ERIE AND OHIO BASINS. 



of the Allegheny River. There are other passes at the heads of tribiitaries 

 which are markedly lower than the passes at the head of the drainage basin. 

 The lowest connecting with the Alleghtin}^ drainage is near Cuba, New York, 

 1,496 feet above tide ; but one near the New York and Pennsylvania State 

 line, connecting with Honeoye Creek, a tributary of Oswayo Creek, is only 

 1,600 feet. The lowest pass connecting with the Susquehanna is at Burns, 

 N. Y., 1,210 feet. 



In the southern half of the basin the tributaries are all sruall. The 

 longest eastern one is Angelica Creek, with a length of 25 miles, and the 

 longest western one is East Coy Creek, with a length of 25 to 30 miles. In 

 the northern half there are four tributaries whose length is about 50 miles — 

 Canaseraga and Honeoye creeks from the east and Oatka or Aliens and 

 Black Creek from the west.^ 



The Grenesee River follows, in the main, the line of a preglacial valley; 

 but, as pointed out by Hall many years ago, it makes slight incursions into 

 the west bluff of the old valley at places where the preglacial valley was 

 greatly filled with drift. It was also thought by Hall that the mouth of the 

 preglacial valley was at Irondequoit Bay." The pi-incipal deflections of 

 the stream are between Portage and Mount Morris and in the vicinity of 

 Rochester. The following concise description of the deflection at Portage 

 was presented by Hall at the meeting of the Association of American 

 Geologists and Naturalists in 1843, and reported in the American Journal 

 of Science for that year. A similar description appears in his report of the 

 Fourth District, also published in 1843: 



The river to the south of Portage flow« in the bottom of a broad vallej'' extending 

 toward the north. At Portageville the stream bends around to the left, and, after 

 flowing a short distance nearly south, turns to the north and northeast, cutting its 

 channel through the rocky slate in some places to the depth of 350 feet, and forming 

 in its passage three falls of 66, 100, and 96 feet, respectively. This channel is narrow, 

 with mural banks; but a short distance below the lower falls it emerges into a broader 

 valley in a line with the channel to the south of Portage before it is deflected from its 

 course. The space between these two points is a deep, broad gorge, filled to a great 

 height with clay, sand, and gravel. This is evidentlj^ the ancient channel of the river, 

 and j^et, after it had become filled with this drift, the stream found an easier passage 

 by excavating the solid rock for .3 miles than by removing these loose materials. 



Still below this point the river leaves the broad channel and excavates a gorge 

 through the shales, emerging into the broad valley at Mount Morris. 



^ It should be noted that the Genesee Eiver has two western tributaries called Black Creek. 

 The name Honeoye is also applied to two streams here discussed. 



2 Geology Fourth Dist. of New York, by James Hall, 1843, pp. 344, 422. 



