SALT ENTERPRISE IN MICHIGAN. 279 



the most elaborate account of the peninsula which was 

 destined to be published for twenty years a confusion of 

 facts which rendered the geology of Michigan an enigma 

 to everyone who attempted to parallelize the rocks with 

 those in the surrounding states.* The following is Mr. 

 Hubbard's tabular statement of the succession of groups 

 embraced in the peninsula: 



A. Erratic Block Group, or Diluvium. 



B. Tertiary Clays. 



C. Coal Measures, I and 2. 



D. Sub-carboniferous Sandstones, II, 3. 



E. Clay and Kidney Ironstone Formation, III, 1. 



F. Sandstone, of Point aux Barques, II, 3. 



G. Argillaceous Slates and Flags of Lake Huron, III, 1. 

 H. Soft, Light-colored Sandstones, II, 3. 



I. Black, Aluminous Slate, III, 1, b. 



K. Limerocks of Lake Erie, III, 2 and 3. 



In this table tire numerals affixed at the right indicate 

 the equivalents given in the table of formations as now 

 established (p. 268). It will be seen that Mr. Hubbard's 

 table makes no separate mention of the formation known 

 as the Michigan Salt Group. But, on the contrary, other 

 formations are three times repeated. The groups marked 

 D, F and H are but different outcrops of the Marshall 

 Group (known in Ohio as the Waverley Group) ; and those 

 marked E, G and I but different outcrops of the Kidney 

 Iron, or Huron Group. Following Dr. Hough ton in the 

 report of 1838, Mr. Hubbard regarded the Point aux 

 Barques sandstones and conglomerates as occupying a 

 position beneath the Kidney Iron formation of the south- 



* See, for instance, Professor James Hall's Report on the Geol. of the Fourth 

 District of New York, p. 519. The present writer explained the causes of this 

 confusion in an article in the Proceedings of the Amer. Phil. Soc.< xi, 59, 60, 

 March 5. 1869. 



