AMKRICAN GEOLOGY MAOLUREAN ERA, 1785-181!). 



243 



In 1821 he was a member of a second expedition authorized by the 

 General Government to explore the central portions of the Mississippi 

 Valley, the results of which were published in 1825. In 1822 he also 

 reported to the General Government on the extent and value of the 

 mineral lands on Lake Superior, and again in 1832 " resumed and 

 completed" his explorations of the sources of the Mississippi, his 

 results appearing- in book form in 1855. 



The expedition of 1820 (See map, fig. 7) started at Detroit and made 

 its way northward along the western shores of lakes St. Clair and 

 Huron to the Straits of Michilimackinac, thence northward through 

 St. Marys River and along the south shore of Lake Superior to Fond 

 du Lac, up the St. Louis River, and down the Savannah to Sand}- 

 Lake and lakes Winnipeg and Cassina farther north. The return trip 

 was made down the Mississippi to the lead region near Dubuque, Iowa, 

 and thence northeasterly up the Wisconsin River to Green Bay. where 



Granite J'oint 



Fig. 9.— Schoolcraft' 8 Section of Presque Isle. 



the party divided, a portion going to Michilimackinac (now Mackinac), 

 along the northern and eastern shores, and the rest keeping to the 

 south, to Chicago, and eastward and north till the starting point was 

 reached once more, one section of the party, with Governor Cass, leav- 

 ing the lake near the southeastern end (at the mouth of the River du 

 Schmein) and going overland to Detroit. 



The narrative of the expedition of 1820 abounds with mineralogical 

 and geological notes, which are in large part, however, of a supposed 

 economic nature. The occurrence of gypsum at St. Martins Island 

 was noted, the island of Michilimackinac itself being of ''transition 

 and compact 11 limestone. A colored section was given showing the 

 relative position of granite and overlying sandstone between Presque 

 Isle and Garlic River (tig. !>). The sandstone he described as overlap- 

 ping the granite and fitting into its irregularities in a manner that 

 "shows it to have assumed that position subsequently to the upheav- 

 ing of the granite." The age of this sand rock lie was unable to satis- 



