THE AJRCH^EAN ROCKS. 



471 



827 



838 



Silica 



Alumina 



Oxide of iron 1 . 93 .... 



Lime 



Magnesia 



Potash 1.84 2.65 



Soda 27 .21 



Water . .... 7.96 



2.95 

 .83 



Fine clay 



Coarse residue. 



54.86 



28.87 



2.48 



.16 



.98 



2.57 



.07 



9.98 



99.97 



56.61 

 43.39 



100.00 



826 A and 826 B are the raw and washed kaolin from Mr. Canning's well; 827 is 

 washed clay from the two pits on the same land, several hundred feet from the well; 



828 is the fine clay levigated from an ex- 

 ceedingly white unbaked brick, said to have 

 been made from clay from Mr. Canning's 

 well. 



The next rock and kaolin occurrences 

 that we note in ascending the Wisconsin 

 are those in the vicinity of the cities of 

 Grand Rapids and Centralia. The localities 

 are shown on the sketch map, Fig. 5. 



Here the river makes a long series of wild 

 rapids over gneissic rocks, which on the 

 shores, at short distances from the water, 

 appear at several points altered to kaolin 

 and overlaid by a few thin layers of sand- 

 stone. 



One of the most instructive occurrences in 

 the vicinity is to be seen on the roadside in 

 J> the city of Grand Rapids, near the Rablin 

 House (Point A on Fig. 5). Here some cut- 

 ting has been done into the bank for grad- 

 ing the street, and kaolin, decomposing 

 rock, and overlying sandstone laid bare. 

 The following is the section obtained here 

 (Fig. 6.) 



A specimen of decomposing gneiss (816), 

 occurring beneath the sandstone, yielded : 



Potash 7.16 



Soda 5.02 



Water 3.55 



The very partial nature of the decompo- 

 sition is thus rendered evident. In appear- 

 ance however, nearly all resemblance to the 

 original rock has been lost, the color being 



< 02 



M 



