492 GEOLOaY OF CENTRAL WISCONSIN. 



banding. A complete arch is to be seen on the east bank of the river in front of Mr. 

 Pitts' house. The plane of the bank, which at this point is about 15 feet in height, cuts 

 directly across the strike, and slopes towards the northwest at an angle of 45. Its base 

 joins another surface sloping about 10 in the same direction. Along both surfaces the 

 individual layers can be traced until they meet near the top of the bank. The central 

 part of the fold as seen on both surfaces is a confused and largely kaolinized felspathic 

 mass (994). 



On the N. E. qr. Sec. 21, T. 23, R. 3 E., Rocky Run enters Yellow river, which hero 

 traverses for many rods a rocky gorge, below which exposures continue along the river 

 for a long distance. About half a mile below the mouth of Rocky Run, gneiss is ex- 

 posed, striking N. W. and dipping E., and traversed by a vein 3 feet wide of a fine- 

 grained, black, hornblendic rock. The vein cuts diagonally the lamination lines of the 

 gneiss. Beginning about twenty rods below the mouth of 'Rocky Run, and extending 

 up to it, are ledges of a fine-grained, greenish-grey, micaceous granite (974), which con- 

 sists of very fine greenish-black mica, predominating, translucent quartz and pink or- 

 thoclase. In places occurs a more highly felspathic, reddish kind (975), which appears 

 sometimes to enclose portions of the darker colored variety. No definite bedding struc- 

 ture was observed. Traversing this granite are numerous thin veins % to % inch 

 in width, of white quartz, pink, cleavable orthoclase, and greenish epidote. The felspar 

 veins are in places so numerous as to make up a large portion of the rock. The epidote 

 veins fault the others, being apparently the most recent. Fig. 19 represents a face 3 



feet by 1% feet. Nearly all of this rock 



1 10. 19. shows a decided tendency to weather, be- 



ing in places altered to an impure kaolin. 

 Kaolin is reported to occur in quantity at 

 points in the vicinity. From the crumb- 

 ling condition of the rocks, this would seem 

 very probable. 



Five miles north of Pitt's Mill, in 

 the northern part of Sec. 3, T. 23, R. 3 E., 

 the bed of Yellow river is made for 15 

 rods of a coarse-grained, flesh-colored gran- 

 FAULTED VEINS IN GRANITE, YELLOW RIVEK. ite ' consisting of a very uniform admixture 



of flesh-colored orthoclase, glassy quartz, 

 and black mica. No distinct bedding is to be seen. 



At Big Bull Falls, nine miles north of Pitt's Mill, on Sec. 15 and 16, T. 24, R. 3 E., 

 large exposures of medium-grained, highly felspathic, red granite extend along the 

 bed and in the banks of Yellow river for a quarter of a mile. This granite has a base 

 of cleavable reddish orthoclase, throughout which is quite uniformly distributed hyaline, 

 occasionally smoky, quartz, in irregularly shaped patches ^ 2 d to ^th inch in diameter. 

 Mica is present, but is very fine and sparse. For the whole length of the exposure, this 

 rock is nearly uniform, and without any tendency to kaolinize. Its peculiar texture, 

 composition and color combine to make it a very valuable and unusually handsome 

 building granite. Polished specimens of the rock attracted great attention at the Phila- 

 delphia Exposition, where it was regarded by experts as among the finest of the many 

 polished granites exhibited. 



On Sec. 7, T. 24, R. 3 E., another exposure of a similar red granite was noted. Above 

 this point, Yellow river is reported without exposures. 



