THE ARCHAEAN ROCKS. 43 j 



dark-brownish, and rough, and has underneath a whitish kaolinized crust. Throughout 

 small white kaolin patches occur. This rock closely resembles that on the west side of 

 Conant's rapids (778). In the bank above, sandstone is exposed. 



Under the central abutment of the railroad bridge, and about 100 feet northwest from 

 the exposure last described, occurs another of the same rock, but somewhat coarser and 

 less predominatingly micaceous. The bedding is the same as before. 



About 300 feet further across the strike, and now on the west side of the river, point 

 X of map, is a large exposure of the same mottled micaceous gneiss, extending several 

 hundred feet along the river bank. At the lower end of the exposure, the felspar sur- 

 faces are very large and very finely striated (787), and the rock is more weathered than 

 usual, the ordinarily brilliant black mica being largely changed to a brownish tint, 

 which affects the appearance of the whole rock. Reddish veins, composed almost en- 

 tirely of coarse, cleavable felspar, occur, and also others in which the felspar is coarsely 

 mingled with wlu'te quartz. The character of the rock remains the same throughout 

 the length of the exposure, as far north as the wagon bridge, the bedding throughout 

 being very distinct, and showing a strike of N. 75 E., and a dip of 45 N. W. A short 

 distance west from the river bank, at this place, horizontal sandstone is exposed in the 

 railroad cutting and in a large quarry. 



The crystalline rock series at Conant's rapids and Stevens Point may be briefly de- 

 scribed as consisting of beds of highly micaceous gneiss, dipping northwest from 45 

 to 80, trending N. 25 to N. 65 E., with which are interstratified some layers of a 

 finer grained, less micaceous gneiss, and penetrating which are reddish granite veins 

 and masses. Compared with the gneisses of Grand Rapids, those just described are 

 found to be more highly micaceous and usually coarser grained. They differ from the 

 Grand Rapids rocks also in having as a prominent constituent a triclinic (striated), 

 whitish felspar, and in having no interstratified beds of dark-colored, fine-grained horn- 

 blendic rocks. The Grand Rapids rocks dip southeastward, those of Conant's rapids 

 and Stevens Point, except at the southernmost point, northwestward, the strikes in 

 both cases being northeast, but not always equally so. The anticlinal line cannot be far 

 from the great bend and long southwestward stretch of the Wisconsin in southern 

 Portage and Wood counties, and to this anticlinal line the peculiar change in the course 

 of the river evidently bears a close relation. See, in this connection, Atlas plate XV of 

 Area F, and its accompanying north and south section. 



On Plover river, in the N. E. qr. of Sec. 12, T. 24, R. 8 E., three quarters of a mile 

 north of Jordan, is a low ledge of moderately coarse, pinkish, porphyritic granite (806). 

 The felspar is in facets up to % inch in diameter, both white and pink, the former finely 

 striated; the quartz is both hyaline and abundant; the mica is in medium-sized, brilliant, 

 black flakes. Numerous white kaolin patches indicate a tendency to decompose. 



On the line of the Wisconsin Central Railroad, between Stevens Point and Junc- 

 tion City, are several small rock cuttings. One of these, on Sec. 22, T. 24, R. 7 E., is 

 in a pinkish, fine-grained granite (800), showing pink and white felspar, quartz, and 

 fine black mica. Another, one mile below Junction City, on Sec. 1, T. 24, R. 6 E., is in 

 a decomposing, medium- grained to fine-grained, whitish-weathering gneiss (801, 802, 

 803, 804), composed chiefly of quartz and pinkish felspar in blotches, with a greenish, 

 greasy mineral (chlorite or altered mica) on surfaces and in fine strings throughout. 

 Pyrite is present, and white kaolinized blotches are characteristic. The more decom- 

 posed portions show a schistose tendency, and in all there is a marked parallel grain. 

 The bedding structure shows a strike of N. 22 E, and a dip of 80 E. These are also 

 the directions of the grain of the rock. On Sec. 2, half a mile from Junction City, is a 

 small exposure of a decomposed brick-red, ferruginous, schistose gneiss (805), showing 

 nn the interior numerous shining mica flakes, but too far altered to show any other 

 minerals. 



Wis. SUR. 31 



