THE ARCH^AN ROCKS. ^„. 



dark-brownish, and rough, and has underneath a wliitish kaoKnized crust. Tlirousrhou^ 

 small whate kaohn patches occur. This rock closely resembles that on the w stsfdeS 

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

 Under the central abutment of the raihroad bridge, and about 100 feetnorthwest from 

 . the exposmrc la.t described, occurs aiiother of the same rock, but somewhat cTsei ^d 

 lesspredomonatrngly micaceous. T^e bedding is the same L before 



About 300 feet farther a/:ross the strike, and now on the west side of the river point 

 X of map IS a large exposure of the same mottled mica^ous gneiss, extending several 

 hmidred feet along the nver ba^k. At the lower end of the exposure, the felspax sur- 

 faces are veiy laxge a^d very finely striated (787), and the rock is more weathered tha^ 



Ti' «■' r'J°^^^ '"^^''* ^'^^'^ "^'-'^ ^'^^ l^^^ly "'^^"gs'l to a brownish tmt 

 ■which aftects the appearance of the whole rock. Reddish vems, composed almost en- 

 turely of cbarse, cleavable felspar, occur, aad also others m wHch the felspar is coarsely 

 mmgled with wHte quartz. The ctoa^ter of the rock remains the same tliroughout 

 the length of the exposmre, as far nori^h as the wagon bridge, the bedding tluwughout 

 bemg 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 crystaUine 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 46° 

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

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

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

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

 Grand Rapids rocks also m having as a promhient constituent a tricHnic (striated), 

 whitish felspar, and in ha-s-ing no interstratified Ijeds of dark-colored, fine-grained hom- 

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

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

 both cases heiag northeast, but not always equaUy so. The anticlinal Une cannot be far 

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

 Portage and Wood counties, and to this anticlinal hue the pecuhar change in the course 

 of the river evidently bears a close relation. See, m tlais conneption. Atlas plate XV of 

 Area P, and its accompanying north and south section. 



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

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

 The felspar is in facets up to J^ inch in diameter, both wliite and pink, the foi-mer finely 

 striated; the quartz is both hyahne and abundant; the mica is in medium-sized, biiUiant, 

 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 kaoHnized blotches are characteristic. The more decom- 

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

 Tlie 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 rrule from Junction City, is a 

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

 on the interior nmnerous shining mica flakes, but too far altered to show any other 

 minerals. 



Wis. Sub. — 31 



