THE LOWER SILURIAN ROCKS. 565 



Near Point Bass, on both sides of the river, heavy ledges of sandstone overlie gneiss 

 (see Figs. 2, 3 and 4). On the east side of the river the sandstone cliff is 30 to 40 feet 

 high. On the west side, near the north line of Sec. 15, on a side channel of the river, 

 dry at the time of our examination, 5 feet of very friable, coarse, brownish sandstone 

 shows in the bank, the upper layer heavy, the lower ones thinner. The bottom of the 

 channel is formed of large flat slabs of the same sandstone, one inch thick. Beneath four 

 one inch layers of this sandstone are two inches of sandstone highly charged with the 

 greenish-tinged iron sulphide, marcasite, which in places almost entirely excludes the 

 sand. Specimens taken oat decompose to the sulphate very rapidly. Immediately be- 

 low, and in contact with, the pyr tous layer, is the Archaean gneiss, much decomposed, 

 but retaining still its firmness and bedding. 



Three-quarters of a mile east of Mapleworks, on the S. E. qr. of Sec. 12, T. 24, R. 

 1 E., Clark county, is an isolated sandstone bluff 100 feet high, 500 yards in diameter at 

 the base, 100 yards long and 10 wide at top, rising above the general level of the divide. 

 The slopes are covered with clay and fragments of sandstone. At the summit 5 feet of 

 very coarse grained, rather firm, brownish sandstone (982) is exposed, consisting of very 

 much rolled grains of dull white quartz. The layers are 6 to 18 inches in thickness. 



About one mile north of Neillsville, on the S. W. qr of Sec. 11, T. 24, R. 2 W., 10 

 feet of cross-laminated, coarse-grained, yellowish sandstone, shows alongside of the 

 road. Clay seams, one to two inches thick, are included between the layers of sand- 

 stone. Similar sandstone is seen at the crossing of Black River, one mile west of Neills- 

 ville, S. W. qr of Sec. 15, T. 24, R. 2 W. The base of the sandstone is 40 feet above 

 the river; below is a slope 10 feet in height, without exposure, and below this, again, 

 30 feet of light-colored pinkish granite. 



Along Black River, from Neillsville to Black River Falls, T. 21, R. 4 W., Jackson 

 county, sandstone is quite frequently exposed in or near the banks of the river, the bed 

 of which is on the crystalline rocks. 



On the S. W. qr of Sec. 3, T. 24. R. 2 W., west of the river, is a sandstone outlier 175 

 feet high, and about one-third of a mile in length, the upper portions of which are per- 

 pendicular ledges of bare rock. The sandstone is heavily bedded, indurated, coarse- 

 grained, and light-colored. From the summit of the bluff a number of other similar 

 outliers can be seen, dotting the country to the west and south, and one or two to the 

 north, in T. 26, R. 2 W. 



For half a mile below French's mill, Sec. 25, T. 23, R. 3 W., the Neillsville road fol- 

 lows the west bank of the river, at an elevation of about 30 feet above the water. On 

 the east side of the road, granite is exposed in the river bank, and on the west side a 

 ridge of horizontal sandstone, 30 to 50 feet high. The sandstone is cross-laminated, 

 coarse, yellowish, and made up of much rolled quartz grains, which reach sometimes as 

 much as one-eighth of an inch in diameter. 



In T. 21, R. 4 W., and T. 22, R. 4 W., ledges of sandstone form the river bank for 

 long distances, rising 20 to 40 feet from the water, and are in a number of places to bs 

 seen overlying, or abutting against, Archa?au schists, as heretofore described (see Plate 

 XVII, and Figs. 1, 2Q and 21). This sandstone is usually of light yellowish color, 

 coarse, and somewhat indurated, and includes beds of red and green sandy shale. The 

 lowest layers are often affected by a very marked cross-lamination, the thickness s6 af- 

 fected being often as much as six to ten feet. 



At Black River Falls, sections 15 and 22, T. 21. R. 4 W., the crystalline rocks are 

 largely exposed, the river passing through a gorge in the gneiss and granite. The 

 ground rises rapidly from the river on both sides, especially the western, and on both 

 sides the granite and gneiss are overlaid by sandstone. At the top of the lull on which 

 the High School building stands, wells pass through 80 feet of sand and gravel into sand- 

 stone. 



