SALT ENTERPKISE 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: Notice of the 

 Rnrkx lijing between the Carboniferous Limestone of the Lower Peninsula of 

 Mirliitjiin. and the Limestones of the Hamilton Group, ivith Descriptions of some 

 Cephalopoda supposed to be new to science. Amer. Jour. Science, II. xxxiii. 352- 

 3iii;. May 1863; Sa't Manufacture of the Saginaw Valley, Hunt's Merchants 1 Mag- 

 azine, 209-2:33, Sept 1862 ; On the Saliferous Rocks axd Salt Spring-: of Michigan, 

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

 thf Marshall and Huron Groups of Michigan, Proc. Acad. Nat. Sci., Philadelphia, 

 405-430, Sept. 1862; On the Identification of the CalskiU Red Sandstone with the 

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

 the Yellow Sandxto-ie* lyi'ig beneath the " Burlington Limestone' 1 '' at Burlington, 

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

 related to the formation which servos 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. 



