BLA CK SHALES OF OHIO— GENESEE SHALES OF NE W- YORK. 6 7 



height, which, rising a short distance back from the shore Hne, re- 

 pose on the ledges of the dolomite beds of the Hamilton group 

 described in previous pages. South of Norwood village, the shales 

 come close up to the shore in vertical bluffs of similar height ; 

 the total thickness of strata seen in the bluffs, and in the hillsides 

 rising behind them, is not over 35 or 40 feet. South of Norwood, 

 the black shales are overlaid by light greenish, arenaceous shales 

 which have frequent outcrops along the shore line for 9 or 10 miles 

 southward, but this is all that can be seen of them ; back from 

 the shore, every thing is covered by drift. Fossils were not dis- 

 covered in the light shales. 



The black shales are exposed northeast of Norwood on Pine 

 Lake, and near Bear Creek the railroad to Petosky has laid open 

 several sections through them, showing sparry, globular concretions 

 inclosed ; pieces of Dadoxylon are likewise found there. 



In the ravines of the creeks leading into Mullett Lake and Black 

 Lake, the black shales are frequently exposed. In Thunder Bay 

 district, outcrops are along the south branches of Thunder Bay 

 River. In Town. 31, R. 7, Sect. 19, the large globular concretions of 

 the shale formation are composed of carbonate of iron, and weath- 

 ered specimens transform on the surface into a bright-colored, 

 reddish ochre. A number of years ago some parties opened ex- 

 ploring ditches in search of that mineral paint, but abandoned the 

 project when they found nothing but unaltered concretions of car- 

 bonate of iron below the outer superficial crust which contained 

 the decomposed ochraceous masses. On Squaw Point, and on 

 Sulphur Island near Thunder Bay, the black shales are well ex- 

 posed ; further south toward Harrisville, they are mostly covered 

 by drift, and only here and there in a ravine can an outcrop be 

 seen. On the opposite side of Lake Huron, at Kettle Point, in 

 Canada, the black shales are splendidly exposed, where their super- 

 position on fossiliferous limestones similar to those of Norwood 

 can be seen. In this locality, the spherical concretions in the shale 

 are larger and more abundant than I have seen them elsewhere. 



In the south part of the State, the black shales are not well ex- 

 posed ; the drift, however, contains large quantities of the shale 

 intermingled in the belt which is supposed to be underlaid by the 

 shales, and in all the deep artesian borings the black shales have 

 been found. 



