110 D. F. Lincoln — Glacial Erosion of New York. 



by Mr. IT. Hall to the depth of 186 (?) feet in sand, with- 

 out touching rock ; the site of the well was near the brook, 

 which has cut its gorge to the depth of 100 feet (esti- 

 mated) below the level of the drift at that point, which 

 indicates 300 ± feet of drift in all. At Elmira the valley is 

 two miles and a half wide ; the Erie road runs near the middle ; 

 borings have been made at the Table factory, just west of the 

 road, giving less than 200 feet of gravel, and at the Rolling 

 mills, just east of the road, striking rock at less than 60 and 

 120 feet ; while at the Blast furnace, in the same region, I am 

 informed by a former official that their well could not have 

 gone more than 100 feet in depth before striking rock. These 

 data are all that seem at present available. We may therefore 

 assume that the drift deposits of the valley equal or exceed 

 300 feet in thickness until we approach Elmira, where they 

 probably become less than 200, perhaps less than 100 feet 

 thick. This places the southern end of the valley at 680-780 

 feet above tide = 850-950 feet (in round numbers) above the 

 deep parts of the lake-floor ; the northern end of the valley 

 being about 400 feet above the lake-floor. 



In the valley of the Susquehanna, between Wilkesbarre 

 and Bloomsburg, a similar state of inversion has been shown 

 to exist (2d Geol. Rep. of Pennsylvania, G 7). Wilkesbarre is 

 124 miles down-stream from Elmira ; Bloomsburg is 40 miles 

 further. At Wilkesbarre the existing river deposits have been 

 pierced by boring to the depth of 180 and 185 feet before 

 striking rock, showing the existence of a buried bed at 340 feet 

 above tide ; while at Bloomsburg the rock-bed is exposed in the 

 stream at a height of 450 feet above tide, giving a tilt of 110 

 feet in a direction contrary to the present course of the river. 



The hypothesis of crust-bending is obviously available to 

 explain such differences of level as the above. It seems to 

 me however, that the arguments for the other side are of great 

 importance. There are three principal ones. 



1. The magnitude of the valleys of Seneca and Cayuga 

 Lakes demands an explanation which has not yet been offered. 

 The Seneca valley at its wider and deeper parts greatly exceeds 

 in dimensions that of the Ohio below Pittsburg; this would 

 not be inconceivable, if we supposed both the Susquehanna and 

 the Chemung to have flowed north past Elmira and Geneva 

 Ontario-wards ; but it is less easy to account for a second valley, 

 that of Cayuga Lake, parallel with it at twenty miles' distance, 

 and nearly as large as the first. Further, the character of the 

 valleys of these lakes changes in going south to the moraines ; 

 they become narrower, and assume the aspect of cols. See tig. 3. 



2. A much more important group of objections exists, which 

 may be summed up under the title of Incompatibility of Levels. 



