GEOLOGY OF THE PORT LEYDEN QUADRANGLE 55 



Stream is developing terraces through the old lake deposits of the 

 valley bottom. 



Drainage 



Black river and its tributaries. From Hawkinsville to opposite 

 Denley, Black river is certainly out of its preglacial channel as 

 shown by the gorge cut into the limestones. Its former course was 

 probably about 2 miles eastward along the Paleozoic-Precambric 

 boundary. Between Denley and Port Leyden it is practically in its 

 old channel. Thence to east of Lowville the stream is somewhat 

 west of the preglacial course due to the westward shifting of the 

 Paleozoic-Precambric boundary by erosion during glacial times. It 

 is doubtful if any of the tributaries of Black river, which cut 

 through the delta deposits and into the Precambrics, follow their 

 old channels because they have been superimposed upon the Pre- 

 cambric surface. Thus Moose river has cut through the deep sands 

 and is now engaged in eroding a channel, with gorges and water- 

 falls, into the Precambrics. 



Origin of the " gulfs." The deep gorges which have been cut 

 through the steep eastern front of Tug hill, by tributaries of Black 

 river, are locally known as " gulfs." The chief gorges are occu- 

 pied by Mill, House, Whetstone and Atwater creeks and Roaring 

 brook. Whetstone gulf which is perhaps the most interesting, is 

 about 2 miles long and shows a depth of 300 feet [see pi. 9]. Its 

 walls are very steep sided to almost vertical, especially in the upper 

 end (narrows) where there is just room enough for the stream at 

 the bottom and where erosion is now proceeding most rapidly. • A 

 section showing something like 700 feet of Lorraine and Utica 

 shales is finely exposed in this gorge. The stream emerges from 

 the " gulf " upon the broad limestone terrace. 



During glacial times the shales were eroded back over the lime- 

 stone for a considerable distance, and this caused the development 

 of the steep eastern front of Tug hill. After the disappearance of 

 the ice from the region, all of the east bound streams from Tug 

 hill rushed over this steep slope and began to erode notches into its 

 summit. These notches were rapidly deepened in the soft shale:- 

 to develop the " gulfs," whose heads have since been cut back to 

 their present positions. South of Tug hill the '' gulfs " are not so 

 well developed because the shales, with their preglacial channels, 

 were not cut back by erosion to such a great extent. 



