STATE GEOLOGIST. 19 



able the Huron county gritstones, and arc 

 m the base "i" the Portage Group 



in Ohio. 

 Farther down the ravine air seen twenty 9r thirty feel af 

 le shales, revered with Iron rust and an astringent 

 respect resembling the shales which 

 undei I Huron. [Jnfortunately there is 



do p of founding an equivalency on paleeontol 



evidence Lside from this 1 am constrained to regard the flag- 

 land as on the horizi n of the grit* 

 I Huron. Bui the Cleveland shales 



are regarded by Dr. Newberry as "Hamilton shales," perhaps, 

 • term Hamilton in the extended sense, bo as 

 t<> include all I York strata from the Marcellua to the 



[f the overlying Bhalea and flagstones ef Lake llu- 

 ron, and the underlying argillaceous limestones of Partridge 

 P ,1 into the Hamilton Group, the intermediate black bitu- 

 minous upy the same position. So I had been in- 

 clined tb regard them So I subsequently learned the black 

 b of Enniskillen were at firsl regarded by Mr. Billings, 

 i he afterwards placed them in the Portage Group on the 

 aent of Prof. Hall. This palaeontologist, whose authority 

 is not to be questioned where palesontological evidence is 

 within reach, thinks he lik< uizei in the vegetable 

 impressions of the black shahs ef Michigan, and in their gen- 

 eral physical factory affinities with some of 

 Portage Group. In this state of the case we 

 shall be constrained for the present to regard the Huron 

 Group of Michigan, extending from the conglomerate above 

 ritstones of Buron county, to the top of the argillaceous 

 - of Partridge Pi , as probably representing the rocks 

 of the Portage Group of New Fork. 



Prom the description which has been given of the Huron 



Group in its northern and southern OUtCTOps, it appears that 



; of coarser materials toward the north, 



and probably attain- in that direction, much the th;< !-.< Bl devel- 



