GEOLOGICAL, AND NATURAL HISTORY SURVEYS. 185 



3. 20, 20, N. Point au Gres limestone. Ugbt colored arenaceous, contaiuiug 

 septa ria. 



4. 27 N. Shale. Black, bituminous, containing pyrites. 



6. 28 N. Thunder Bay limestone. Beds of limestone and gray clay or shale, con- 

 taining abundant fossils. 



0. 30, .31 N. Black bituminous limestone. Bituminous, composed of congeries 

 of shells. 



7. 32. 33 N. Blue limestone. Compact and in thick strata. 



8. Mackinac limestone. Very porous, tmd the upper portion much shattered. 



"It will be seen," adds Mr. Doii<;]ass, "tliat the same rock, with 

 one or two exceptions, occurs on both sides of the State, luiving the 

 same geological position; also that they have very nearly parallel 

 and uniform positions. And from the outcrops the rocks Avould ap- 

 pear to have a bearing nearly N. 70° W. and S. 70° E., which line of 

 bearing corresponds with the outcrop of the black bituminous slate 

 on the east side of Lake Huron in Upper Canada" (p. 103). Doc- 

 tor Houghton had already fixed the "line of bearing" northeast and 

 southwest. The INIichigan geologists thus far had not attained to 

 the conception of a dishlike arrangement of the strata. They 

 thought tlie outcrops must strike across the Peninsula, nearly in 

 straight lines. 



The "Manistee limestone" is unknown to the writer [Winchell]. 

 Moreover, the Manistee River, near which in townsliip 15 north, lime- 

 stone is stated in the accompanying text to occur, is located entirely 

 north of township 15. On the other hand, in township 15 and near 

 the Pentwater River in Oceana County, occur masses of limestone, 

 which the writer has referred to the Lower Carboniferous.^ 



The " Shales" in township 31-32 north, outcrop on Grand Traverse 

 Bay and constitute the writer's " Huron group," the black shale be- 

 ing the " Genesee." The " Corniferous limestone " is not definitely 

 located by Mr. Douglass; but in township 33 we find limestone an- 

 swering to the description, outcropping on the lake shore betvv^een 

 the mouths of Grand and Little Traverse Bays. It belongs near the 

 top of the Hamilton group, and its stratigraphical position is cor- 

 rectly indicated. The "Little Traverse Bay limestone" belongs at 

 the bottom of the Hamilton group. The " Black bituminous lime- 

 stone" is not considered by the writer to occur at a lower horizon 

 than the last, but between it and the so-called "Corniferous." The 

 " Blue limestone," also is embraced in the Hamilton. 



As to the rocks of Lake Huron, the "Poiiit au Gres limestone" 

 is an arenaceous stratum in the lower part of the Lower Carboniferous 

 limestone. The "shale" is the black Genesee shale. The "Thunder 

 Bay limestone " belongs in the loAver part of the Hamilton, and the 

 " Black bituminous limestone " holds a higher — not a lower — position. 



^ Winchell, Proc. Amor. Assoc, 1875, p. 36. 



