500 GEOLOGY OF CENTRAL WISCONSIN. 



white quartz, partly arranged in separate white bands, up to one inch in width, 

 and partly also mingled with fine, brilliant black mica, and fine, white felspar, in 

 dark gray bands. The weathered surface of this is dark brown with a white kao- 

 linized undercrust. North of the gneiss no rock occurs for 400 feet, then come 

 outcrops some 500 feet long of, 



n. Diorite (1,003): rather coarse-grained, highly crystalline, grayish, felspathic; com- 

 posed of large surfaced, bluish-gray felspar, with coarse hornblende; without def- 

 inite bedding structure. Underneath the railroad bridge this rock is terminated 

 by a mass or vein of, 



III White quartz: 5 feet wide. Immediately next to which begin outcrops about 200 

 feet long of 



IV. G;7m'6' (1,005 and 1,006): rather fine-grained, pink- and-gray-banded, very quartz- 

 ose; consisting principally of pink and colorless translucent quartz, with some fine 

 gi-eenish-black mica and pinkish, orthoclase; in places a quartzite (1,004), the oth- 

 er minerals being almost wholly absent. Above this the rocks are concealed for a 

 short distance, after which are seen, some 20 feet in width, of 



Y. Micaceous schist (1,007).: a very peculiar, fine-grained, dark-brown, earthy-textured, 

 jointed rock. Under the lens it is seen to consist largely of angular grains of 

 quartz. The smooth jointed planes of this rock strike N. W., and stand vertical. 



In the river one mile above Rlaok River Station, a ledge 150 feet long and 25 feet 

 high, is seen, of fine-grained, dark-reddish granite (990), consisting of a rather uniform 

 and close admixture of reddish orthoclase, in fine ghttering facets, reddish-brown, trans- 

 lucent quartz, some colorless quartz, and a little, sparsely scattered, fine black mica. 

 Half a mile further up stream, fine-gi'ained, red and gray banded, quartzose gneiss 

 (991) is exposed. The gray bands consist of fine-grained, glassy quartz, fine black mica 

 and wliite felspar; the red of brovsm and red translucent quartz, mingled with a httle 

 orthoclase. From here to the mouth of the East Fork, the bed of Black river shows nu- 

 merous small ledges, 3 to 4 feet high, of contorted gneiss and reddish granite. 



Above the mouth of the East Fork, which is on Sec. 36, T. 23, R. 3 W., exposures 

 of red granite are seen as far as French's mill, on Sec. 25. The wagon road which, 

 for half a mile below the miU, follows the west bank of the river has, on the east side, 

 ledges of red granite, and on the .west, a ridge thirty to forty feet high, composed of 

 horizontal, coarse-grained, quartzose, cross-laminated sandstone. In one place, the 

 exact junction of the two formations is to be seen. At the mUl, the granite exposures 

 are especially large, both on the west bank and on a large island in the stream. Two 

 lands of the granite occur, both presenting a prevailing pinkish weathering : (1) a rather 

 fine-grained, very uniEorm- textured, dark reddish kind (988, close to 990); and (2), a 

 medium-grained, unifonn-textured, pmldsh-grey, quartzose kind (987), containing 

 both colorless glassy, and pink translucent quartz; pink orthoclase; and fine black 

 brilliant mica. Both kinds appear hke handsome building or ornamental granites. No 

 definite bedding structure is to be seen. 



On the wagon read, three quarters of a mUe south of Neillsville, Sec. 22, T. 24, R. 

 2 W., is a large outcrop 200 yards long, and 10 to 40 feet high, of porphyritie, cal- 

 careous gneiss, striking E. W., and clipping 80° S. At the northern end of the ex- 

 posure, the rock (984), is anedium-grained, fine-laminated, Imotty, and highly mica- 

 ceous. Fresh surfaces show a large quantity of fine-flaked brilliant black mica, white 

 quartz in little nests, around which the micaceous laminse curve, and white felspar, 

 which sometimes occurs in smaller nests up to a quarter to half inch in diameter. In 

 large quantity, the pulverized rock effervesces briskly in muriatic acid. In the middle 

 portion of the ledge, the rock (985), closely resembles that just described; but shows 

 much pmk cleavable felspar and less mica, the pink felspar forming the knots. At the 



