STATE GEOLOGIST. 49 



and near the mouth of Chocolate river, and extend westward to 

 join another belt beginning a few miles south of Huron river. 

 The first belt in the neighborhood of the Machigamig river, 

 suddenly expands towards the south, so that on the State 

 boundary the Azoic belt stretches from beyond Lac Vieux De- 

 sert to Chippewa Island, in the Menomonee river. It extends 

 thence westward through Wisconsin and to the sources of the 

 Mississippi. The rocks of this system consist in Michigan of 

 talcose, chloritic and silicious slates, quartz, and beds of marble. 

 The silicious slate, becomes, near Marquette, a novaculite, from 

 which hones have been manufactured. In this system are found 

 the specular and magnetic iron ores of. Lake Superior, as well 

 as of Pilot Knob, and perhaps the Iron Mountain, in Missouri, 

 the Adirondacks of New York, and other localities. This series 

 of rocks attains an enormous thickness on the northern shores of 

 Lakes Superior and Huron; and Sir Wm. Logan, the Director of 

 the Canadian Geological Survey, has decided that they consti- 

 tute two great systems, unconformable with each other, the 

 upper of which he styles the JBuronian series and the lower the 

 Laurenlian* The Bruce, Wellington, and neighboring mines, 

 are located in these rocks, and are worked for the ores of cop- 

 per; while the Lake Superior mines are located in veins which 

 belong to the age of the trap, and are worked for native copper 



IV.— FOSSILIFEROUS .STRATA. 



I. LOWER SILURIAN SYSTEM. 



1. — Lake Superior Sandstone. 

 The reddish, yellowish, grayish or mottled sandstone, found 

 along the south shore of Lake Superior has, by different wri- 

 ters, been assigned to different geological periods; 1 ut the 

 weight of authority is decidedly in favor of placing it at tho 

 base of the Palaeozoic series, and on the horizon of the Potsdam 

 Sandstone of New York. Further examinations will undoubt. 



* Report 1852-3, p. 8; 1S5G, p. 171. 



