524: GEOLOGY OF CENTRAL WISCONSIN. 



The exposures on the mam hill are mostly on the eastern and southeastern portions 

 where in places they rise nearly precipitously from the low ground at foot. The rock 

 seen here is for the most part (1354) a glassy, translucent, subgranular, grayish quartz- 

 ite, much more nearly aUied to the quartzite of Rib and Mosinee hills in Marathon 

 county, than to that of the Baraboo ranges. Much of the rock is quite dark-gray in 

 color, the quartz then being still glassy but smoky-tinted. Numerous small cavities 

 and seams occur, lined witli half crystalUne quartz, and carrying a soft, pmkish, clayey 

 substance; bluish-white quartz veins (13551^) one-half to two inches in width, and 

 nests, are also common, and these carry frequently fine-flaked, brilliant, specular u-on, 

 which occurs also occasionally m quite large masses, similar to those found ia the Bara- 

 boo quartzite. No parallel grain is to be seen in this rock, nor any definite bedding 

 planes. Numerous quite close joints occur, however, and these cause the rock to weath- 

 er into smooth-faced, sharp-angled fragments. On the smaller bluff a very distinct 

 parallel grain is to be seen trendiag N. 75° W., and showing a corresponding dip of 

 4-3° N. Here much of the quartzite is of a light pink color, looking, on a fresh fractm-e, 

 almost like a fine-grained, pinkish granite (1358;, but the only prominent nnneral is sub- 

 granular, translucent, pinkish quartz. Some specimens show mica plainly in veiy 

 sparsely scattered, small scales. In many places little centers of iron-staining seem to 

 be decomposing mica scales. Other portions of tliis rock (1358, 1357) are opaque, white, 

 and distinctly granular, and are seamed with fine black lines, arranged so as to show 

 discordant stratification. These seams when spht open, appear to be composed of 

 blackish mica. Bluish-white veins and nests occur here also. 



