SALT ENTERPRISE IN MICHIGAN. 267 



The outbreak of civil war interfered with the organized 

 prosecution of field work during 1861 ; but the State 

 Geologist found abundant occupation, an important part 

 of which consisted in the office and laboratory investiga- 

 tion of the materials accumulated during the two pre- 

 ceding years.* 



Let us understand now what the researches of 1859-61 

 succeeded in establishing. They showed that the forma- 

 tions of the lower peninsula of Michigan constitute a series 

 of successively overlying dish-shaped structures, with mar- 

 gins approximately concentric with each other and with 

 the boundaries of the peninsula. The uppermost rock 

 formation occupies nearly the central part of the penin- 

 sula, and has less geographical extent than any of the 

 others. This is the Coal Measures, consisting of a sand- 

 stone at or near the top, and another named the Parma 

 Sandstone at the bottom. Next below is the Carbonifer- 

 ous Limestone, the outcropping border of which is some- 

 what farther from the center of the peninsula. Next is 

 the Michigan Salt Group, which actually underlies the 

 whole central part of the peninsula, and outcrops at 



* Some of these scientific results were published as follows: Ifotice of the 

 Rocks lying between the Carboniferous Limestone of the Lower Peninsula of 

 Michigan and (he Limestones of the Hamilton Group, icith Descriptions of some 

 C'ephalopods supposed to be new to science, Amer. Jour. Science, II. xxxiii, 352- 

 3M. May 1862; Sa't Manufacture of the Saginaw Valley, Hunt's Merchants' Mag- 

 azine, 209-223, Sept 1862; On the Saliferous Rocks and Salt Springs of Michigan, 

 Amer. Jour. Science, II. xxxiv, 307-316, Nov. 1862; Descriptions of Fossils from 

 the Marshall and Huron Groups of Michigan, Proc. Acad. Naf? Sci., Philadelphia, 

 405-430, Sept. 1862; On the Identification of the Calski'l Red Sandstone with the 

 Chemung, Amer. Jour. Sci. II, xxxv, 61-2, Jan. 1863; Descriptions of Fossils from 

 the Yellow Sandstones lying beneath the "Burlington Limestone" at Burlington, 

 Iowa. Proc. Acad. Nat. Sci.. Philadelphia, Jan. 1863. pp 2-25. These articles all 

 related to the formation which serves as the reservoir of the brine supplying the 

 principal wells along the Saginaw River, and were contributions toward fixing 

 its geological age and characteristics. Other investigations were published at 

 later dates. 



