328 



which are imbedded nodular masses of kidney ironstone. This is a 

 rich and valuable oie and occurs at several points conveniently for wor- 

 king. 



This formation is the lowest that is discoverable in this portion of the 

 State, and is not certainly known to make an outcrop elsewhere. 



For fuither description of this clay and its contained ore, I refer you 

 to the Annual Report of the State Geologist of 1840, and to my own, 

 appended thereto, for many practical considerations relative to the value 

 of the ore and its imbedding clay. This formation is marked F, in the 

 plate. 



SANDSTONES OF POINT AUX BARQUES. 



These are mostly a coarse, greenish gray or rusty yellow rock, in 

 some of the layei-s approaching a conglomerate. They form cliffs along 

 the shore of Lake Huron, in Huron county, rising at Point aux Barques 

 to twenty feet. Fossils are rare, but Atrypa and Calymene were ob- 

 tained. These sandstones occupy the coast north of town seventeen, 

 being visible in ledges for about twenty miles. The upper portion of 

 the series contains numerous, small imbedded pebbles of quai-tz, so as to 

 resemble a conglomerate or puddingstone, but no great thickness is ob- 

 servable, of rock possessing this character. 



An extension of the outcropping edge of these sandstones, it is prob- 

 able, gives rise to that swell of land which forms the summit level of 

 the Peninsula, stretching in a south-westerly direction from Point aux 

 Barques to Hillsdale county, where the green and yellow fossiliferous 

 sandstones, above described, overlie it. But throughout this whole ex- 

 tent no outcrop of the rock is visible, owing to the thickness of the di- 

 luviums. 



These sandrocks, taken in connection with the formation next descri- 

 bed, hold a place in the Geological series, corresponding to the " waverly 

 san dstones," and " conglomerate," of Ohio, but the deposition seems to 

 have been made under somewhat differing circumstances. No well de- 

 fined series is apparent in our State, answering fully to the Ohio con- 

 glomerate ; though the upper portion of the sandstones of Point aux' 

 Barques ajipruach that character. 



The whole thickness of th^e sandstones probably exceeds 250 feet. 

 This group is marked F, in the plate. 



