56g- GEOLOGY OF CENTRAL WISCONSIN. 



Opposite Ledyard's old mill (Fig. 20), in the bend of the river below the village, 25 

 feet of sandstone overlie the gneiss. The sandstone here is the usual coarse crumbly 

 rook, and includes layers of greenish and reddish shale, the lowest layer being a fino 

 conglomerate, 8 mohes in thickness. 



Near tlie railway depot, on the west side of the river, is a quarry in the sandstone 

 layers belonging just above those exposed at the mill. The quarry fade is 15 feet liigh, 

 and travei-stid by strong vertical joints. The stone (1012) is heavily bedded, much in- 

 durated, of a light color, and composed of alternating very coarse and finer grained 

 layers, all bemg composed of rolled grains of glassy quartz. Some of the layers show 

 cross-lamination. This stone is a valuable one, and resembles that from the quarries 

 already alluded to as occumng near Grand Rapids and Stevens Point. 



About a mile southeast of the depot, on Sec. 23, is ^ very bold sandstone outlier rising 

 aiwut 250 feet above its base. In the lower slopes tlie sandstone is mostly concealed. 

 Above is a perpendicular-faced, jagged crest, over 100 feet in height, the prevailing 

 rock (1013; on which is a white to buff-colored, iine-grained, firm sandstone, composed 

 of sub-angular to rounded quartz-grains, and containing near the top numerous u-on- 

 stained impressions of Oholella pnlita, but no shells. 



About one mile west of Black River Falls, on the road westward to the IVempealeau 

 valley, is an exposure of thin-ljedded, coarse, brownish, crumbling sandstone (1010), 

 with numerous white fragments of shells of Oholella polita, which, in some of the layers, 

 make up most of the rock. Thin clayey layers occur in which a few shells were noticed, 

 one of Lingiilepis pinnceformis. The outcrop appears to be 130 to 150 feet below the 

 Oholella sandstone of the bluff near the depot. . 



In the various exposm-es in the vicinity of Black River Falls, we have a total thickness 

 of sandstone of about 350 feet, with two fossil horizons made out, one 200, the other 300 

 feet, above the gneiss base upon which the pile rests, and both showing Oholella polita. 



On the west side of the Trempealeau valley, Sec. 2, T. 22, R. 5 W., Jackson county, 

 is a pecuhai- isolated bluff known as the Silver Blutf. At the east end the bluff is 

 165 feet liigh, the lower slopes being covered with a talus from the ledges above. Near 

 the summit is exposed a horizontally and very plainly bedded, hard, white quartzite (1011), 

 wliioh rings like steel when struck with the hammer. The layers are alternately tliin 

 and tliick, and brownish-weathered, and include interstratified layers of friable sand- 

 stone. The quartzite shows distinctly lines of lamination, and has a very plain granular 

 texture, being composed of grains of vitreous quartz wliich appear as if fused together, 

 and is quite highly translucent. It is unlike the quartzite of the Baraboo ranges, or 

 that of the hUls near Wausau, Marathon county. It contains very abundant fi-agments 

 of casts, more rarely perfect casts, of a very large conical foksil which Mr. Whitfield de- 

 termines as a new species of PalceacmcBa. Following the bluff along the brow of its 

 southwest face, the quartzite layers are seen to continue for about a third of a mile, 

 when a sudden rise in the blufil' of 80 feet exposes tiim-bedded, firm, dark reddish- 

 brown, liighly ferruginous, sandstone (1016), of a medium grain, and composed of 

 rounded grains of glassy quartz, which are stained both externally and internally by 

 iron-oxide. On the north flank of the hUl, at the same elevation as the quartzite on the 

 opposite side, an 8 inch layer of hard, white quartzite is seen, between heavy beds of 

 whitish friable sandstone. 



Juneau and Adams Countiks. 



(Atlas Plates XIV and XVIII, Areas E. and H.) 



Those two counties constitute a rectangular-shaped district, lying in the' vei-y heart of 

 the state, about 42 miles from north to south, by 36 from east to west, and having an 

 area of about 1,475 square miles. Throughout the whole area, except on the Small 



