D. F. Lincoln — Glacial* 



Art. XIV. — The Amount of Glacial Erosion in the Fmger- 

 lake Region of New York; by D. F. Lincoln, M.D., 

 Geneva, N. Y. 



[Read before the Am. Assoc, for the Advancement of Science, Madison, August, 



1893.] 



The Lake-region proper does not extend beyond the De- 

 vonian belt ; it will, however, be instructive to include in 

 our consideration the closely-related " drumlin-belt" of level 

 country adjacent on the north, which covers the upper Silurian 

 area between Rochester and Syracuse, nearly. Within this region 

 occurs the well-marked, though low, Corniferous escarpment, 

 besides some local escarpments to the south : the Niagara 

 exposures being hardly worthy of that name. Most of the 

 formations are exposed at great numbers of points in brooks, 

 and complete sections across the Devonian are afforded by 

 some of the lakes. Beginning at the north, the formations in 

 ascending order are as follows :* 



The Medina sandstone along Lake Ontario is thickly envel- 

 oped with drift and lake deposits. Five exposures in the beds 

 of brooks are mentioned by Hall in Wayne County. (Report 

 for the Fourth District, 1843). In the Clinton shales and lime- 

 stone Hall names twelve exposures, adding that "almost every 

 stream north of the road from Wolcott to Rochester exposes one 

 or more members of this group." The Niagara shale is soft, 

 and forms very gentle slopes. It is exposed, though not deeply 

 cut. in "all the small streams which flow into the lake" (Hall). 



The Niagara limestone occupies a tract a mile or two wide, 

 crossing the middle of the lake counties from west to east. Its 

 position is marked by a line of lime-kilns across the country. 

 Little cascades or rapids occur wherever the streams pass from 

 it to the shale. It is characterized by frequent low anticlines, 

 with axis approximately N.-S., the backs of which come 

 within a foot or two of the surface. Broad levels, underlain 

 by sheets of this rock, with only a foot or two of soil, have 

 been observed at Sodus. On the whole, the contour of the 

 landscape is not distinctly affected by this formation. 



The Salina formation, being to a great degree composed of 

 weak rocks, is probably excavated and buried more deeply 

 than the others. The Clyde, the present outlet of the Finger 

 lakes, runs through it lengthwise (W.-E.) ; for several miles 

 west of Lyons its valley is deserted by its wandering occupant ; 

 the banks are there 30 feet high exclusive of drumlins, and 

 rock is not exposed. 



Distinct evidence in regard to the depth of the drift-cover- 

 ing is less easily had in this formation than elsewhere. The 



*For a sketch map of the Lake region, se? this Journal, October, 1892. 



