58 GLACIAL FORMATIONS OF ERIE AND OHIO BASINS. 



eastern end of Lake Erie eastward past the northern ends of the Finger 

 Lakes to the Hudson River Valley. This group' of rocks forms the foot- 

 hills of the elevated uplands which occupy the southern portion of western 

 New York. 



In Ohio there is onlj^ a thin development of this group of rocks in the 

 central and northern parts of the State. This group may have a thin 

 development in northern Indiana.-' It is thought to be represented in the 

 hydraulic limestone at the Louisville Rapids, on the south border of the 

 State.^ 



Genesee, Portage, and Chemung, or Ohio shale series. Uudcr the UameS GreneSeC, Por- 



tage, and Chemung there are included in New York a complex series of 

 shales with occasional beds of flagstone and sandstone. This series in Ohio 

 appears to be represented by a single great shale formation, now known as 

 the Ohio shale, but designated by the geologists of the first Ohio survey the 

 "shale stratum" or "black slate." The apparently equivalent formation in 

 Indiana is commonly called the "black shale." 



The Genesee shale of western New York bears a striking resemblance 

 to the Marcellus shale in color and general characteristics, but differs from 

 it in fossils as well as in stratigraphical position. It is a thin formation, 

 having a thickness of only 25 feet on the borders of Lake Erie and about 

 150 feet on the shores of Seneca Lake. It appears in the gorge of the 

 Genesee at Mount Morris. 



The Portage of western New York "presents an extensive develop- 

 ment of shale, shales and flagstones, and finally some thick-bedded sand- 

 stone toward its upper part." It has excellent exposures in the gorge of 

 the Genesee at Portage Falls. Hall has called attention to the influence 

 of the sandstone in preserving the high ridges between the deep valleys of 

 western New York, and also to their influence in producing cascades.^ 



The entire thickness of the Portage group on the Genesee is estimated 

 by Hall to be fully 1,000 feet. At the New York-Pennsylvania line 

 it is thought by White to rise 475 feet above Lake Erie, but near the 

 Pennsylvania-Ohio line it passes below lake level.* Its outcrops in Erie 

 County, Pa., are described by White as containing a succession of alternate 



'See Phinney: Eleventh Ann. Kept. U. S. Geol. Survey, Pt. I, 1891, p. 636. 

 ^W. W. Borden: Fifth Ann. Eept. Geol. Survey Indiana, 1873, pp. 150,161,172. 

 = New York Geol. Survey, Fourth Geol. District, p. 225. 

 * Second Geol. Survey Pennsylvania, Kept. Q*, 1881, p. 119. 



