11 M'ISCOXSIjN' ACADEilY SCIENCES, ARTS, AND LETTERS. 



pyrites. Then succeeds a variegated white and yellow sand-stone 

 =ic ^= * -:=" In this aecouDt Dr. Norwood conveys the erroneous 

 impression that the kaolin of the Wisconsin occurs as a bedded clay, 

 which it does not do. 



The various localities at which kaolin has been noticed in the state, 

 so far -as my knowledge extends, all occur in a belt of country about 

 fifty miles in length and fifteen in bread'th, stretching eastward 

 from Black river in Jackson county to the Wisconsin, in the vicin- 

 ity of the city of Grand Rapids, in Wood county. This district in- 

 cludes more or less of townships 21, 22, and 23 north, and ranges 

 1, 2, 3, 4 west, and 1, 2, 3, 4, 5, 6, 7 east,"of the meridian. It is 

 crossed from north to south by three streams of considerable size; 

 Black River on the west, the Wisconsin on the east, and Yellow 

 River towards the centre. The kaolin discoveries have, I believe 

 been made almost entirely in the vicinity of these streams. 



Geologuqf the kaolin district. — The district thus described, lies 

 for most of its extent just south of the main boundary-line between 

 the Potsdam sandstone, which underlies so large an area to the 

 south, east, and west, and the Archaean rocks, which form the 

 sub-structure of all the region to the northward. In places the 

 boundar}'-, which is a ver}^ irregular one, lies within this district. 

 The country in this part of the state is generally level, with a 

 gradual rise to the northward. In the more southern portion of 

 the belt, the sandstone is nearl}^ everywhere the surface rock, ex- 

 cept along the beds of the rivers, where the strata of Archaean gneiss 

 granite and diorite are laid bare. The sandstone is therefore, where 

 it occurs, only a very thin covering over the crystalline rocks, and 

 indeed these occasionally rise through it in bold isolated bluffs of 

 granite and quartzite, which, though sometimes as much as two 

 hundred feet in height, cover but a small area. Interspersed with 

 these are other bluffs of similar height and dimensions, of horizon- 

 tal sandstone, bearing witness to the great thickness of that rock 

 which has suffered denudation. Further north, the gradual rise of 

 the country seems to be due in some measure to the shape of the 

 surface of the underlying Archaean rocks, which finally rise from 

 beneath the sandstone and become the surface formation. The 

 boundary between the two terranes is traced with great difficulty. 

 Barometrical elevations are no guide at all, for the sandstone hav- 

 ing once covered the region so deep]}^ maj^ be found at the very 



