STATE GEOLOGIST. 91 



would, however, constitute a reversal of the general law of our 

 strata, and I have consequently been induced for the present to 

 regard the shale reached in the Saginaw deep well as the thick- 

 ened separating shale lying between the Napoleon and Mar- 

 shall Groups. 



13. — Michigan Salt Group. 



The Napoleon sandstone, exposed along the right bank of the- 

 Grand River a mile or two above Grandville, in Kent county 

 (S. E. \ sec. 7, Wyoming), near the residence of Mr. Davidson, 

 is succeeded upwards by a remarkable series of saliferous 

 shales and intercalated beds of gypsum and magnesian lime- 

 stone, attaining a maximum observed thickness of 184 feet. 

 The lower portion of this formation outcrops in an extensive 

 salt marsh, on sec 3, T. 6 N., 12 West (Wyoming, Kent county). 

 This is the locality of the State salt well, near Grand Eapids. 

 Nearly opposite, on the north side of the river, in a bluff rising- 

 60 or 80 feet above the water, are located extensive gypsum 

 quarries. At the quarry known as McEeynolds & Stewart's,. 

 I observed the following section: 



19. Loam, variable in thickness. 



18. Clay, yellowish and plastic, 3 ft. 



17. Shale, 3 ft. 



16. " Plaster rock" — a series oi irregularly alterna- 

 ting layers of arenaceous limestone and shale, 

 inclosing many masses of reddish gypsum, .... 5 ft. 

 15. Limestone, argillo-arenaceous (called "flint,").. 4 in. 



14. Shale, blue, thinly laminated, pretty uniform, . ... 4 ft. 6 in. 



13. " Water limestone," 8 in. 



12. Shale 1 ft. 



11. Water limestone, 10 in. 



10. Shale, 3 ft. 



9. " Plaster rock," composed of plaster, with some 



clay 2 ft. 



8. Shale, 3 ft. 



7. Water limestone, (which in Hovey's quarry was 



found to pass into gypsum,) 2 ft. 



6. Shale, 3 ft. 



5. Gypsum, 6 ft. 



4. Shale, . '. 9 in, 



3. Gypsum 13 ft. 6 in. 



