THE ARCH^AN ROCKS. 477 



nor B 



Saica 16 . 33 



Alumina 12.03 



Iron oxide 24 



Lime 00 



Magnesia 00 



Potash 12 



Soda 03 



Water 3.75 



8l'.50 



The most ferruginous clays seen at Mr. Garrison's yielded 1.68 per cent. (808), and 

 2.31 per cent. (809) of iron sesquioxide. These are apparently much more plenty than 

 the white clay. About 10 rods from the kaolin openings, on the river edge, is a low 

 outcrop of a highly micaceous, weatheiing gneiss (808). having a moderately coarse, 

 jagged textm-e. The felspar of this rock is largely still brilliant, but Uttle white kaolin 

 patches dot the surface. Another outcrop near by shows a more highly felspathic kind, 

 with very coarse, pinkish orthoclaae. These gneisses closely resemble the prevaiUng 

 ones in the Grand Rapids section, but are evidently much lower in the series than any 

 of those. 



At the Green Bay and Mumesota depot, Grand Rapids, it is reported that in excavat- 

 ing for a turn-table, first a few layers of compact sandstone were penetrated, then 5 to 

 6 feet of soft white clay and decomposed rock. Near the center of Sec. 4, T. 22, R. 6 E. 

 (point E of map), about two miles above Grand Rapids, on the east bank of the Wis- 

 consin, on Mr. Rablin's land, very white kaolin shows, overlaid by two feet of sand- 

 stone. This kaolin has been used with success to line the furnaces at the Grand Rapids 

 foundry. The following are analyses of samples from here: 



829 8S8 1-3 



AS B 



Oxide of iron 4.43 



Potash 1.21 .87 .38 



Soda ji^ ^11 J^ 



829 A and 829 B are raw and washed clay taken from the stock-pile at the foundry; 

 828^2 is washed from a sample taken from the opening itself. 



On the line of the Wisconsin Valley Railroad, between Centralia and Junction 

 City, are several low cuttings, which expose usually crumbhng, and partially decom- 

 posed, laminated gneiesic rocks. The exposures are very poor and the rock is generally 

 out of position. About 3}i mOes north of Centralia is a cutting 400 feet long, tln:ough 

 a rather fine-grained, granular textured, pinkish granite (965). This rock consists of 

 brownish, translucent, giunular, glassy quartz, largely predominating; pinkish bright- 

 lustered felspar; and fine black mica sparsely but uniformly scattered. It would dress 

 readily, but shows some tendency to weather and iron stain. 



West of the raih-oad Hue, in the western part of T. 23, R. 6 E., sandstone occurs in 

 places, sometimes capping the liiRs, sometimes low in the valleys, and lying evidently 

 upon a very irregular ciystalbne rock surface. On Sec. 8, near the northwest comer of 

 the section, a well passes through sand 6 feet, sandstone 2,1^ feet, soft red and white 

 kaolinized rock 20 feet. Tliis is the greatest depth of softened rook that has come to my 

 notice in Wisconsin. 



