206 H. p. GUSHING UNCONFORMITY AT BASE OF BEREA GRIT 



Orton mentions it, and seems to have attributed no more importance to 

 it than did Newberry. Burroughs has described some phases of it in 

 Lorain County, Prosser has treated of it in the central and northern 

 parts of the State, and the writer has been familiar with it for many 

 years, and has long had a description of it as it occurs in Cuyahoga 

 County in a manuscript whose publication has been greatly delayed/ It 

 is an extremely obvious discordance, is at once noted in any good section, 

 and for several reasons the present seems an auspicious time to discuss its 

 significance. 



Description 



Unquestionably this unconformity is most prominent in the district 

 described by Burrows in Lorain County and westward, where the most 

 northwesterly outcrops of the formation in the State occur and where the 

 strike swerves from an east-west to a north-south direction along the east 

 side of the Cincinnati anticline. Here its type is of deep, sand-filled 

 channels cut out in the underlying shales. These reach an extreme depth 

 of from 150 to 175 feet, are fairly steep-sided, and have apparently a 

 width of but a few hundred feet, only from three to five times the depth. 



East and south from this northwest angle the unconformity rapidly 

 loses this prominent character. Considerable channels are present in 

 Cuyahoga County, next east of Lorain, though much smaller than the 

 Lorain examples; but the general character of the contact is that of 

 rather slight irregularity, the surface of the shale being etched with 

 small, shallow channels wliich ai'c filled with sand. In general a thick- 

 ness of less than 10 feet is involved, and usually much less. The in- 

 stances described by Prosser from central Ohio seem all of this type. 



The Brooklyn Channel 



Perhaps the best exposure yet seen in illustration of the miconformity 

 is one on the southwest edge of Cleveland, first studied by the writer in 

 1907, soon after it had been developed by a deep cut made in construc- 

 tion of the Belt Line Railroad. A glance at the accompanying map, 

 figure 1, which is a reproduction of a small portion of the western mar- 

 gin of the Cleveland topographic sheet, will show the 840-foot contour 

 projecting northward in a long, narrow promontory, reaching out three- 

 fourths of a mile beyond its normal line. It forms a prominent cusp 

 which, as seen from the north, constitutes a bold and striking feature of 



* .Tour. Geol.. vol. xix. pp. 655-659 ; vol. xx, pp. 585-604 ; voL xxii, pp. 766-771 ; Bull. 

 15, Geol. Surv. Ohio, 4th series. 



