4Si GEOLOGY OF CENTRAL WLSCONSIN. 



translucent, and beautifully striated, as can readily be seen with an ordinary lens. More 

 rarely pinkish felspar occurs. That variety of this rock which has a medium degree 

 of coarseness presents a very handsome appearance on a dressed surface; and, since 

 it shows no tendency to iron - stain or decompose, might make a valuable building 

 stone. The second variety found here (897, 905, 903) is veiymuch finer m grain, and of 

 a dark.greenish-gray color, showing the crystalline texture only under the lens, and 

 then not plainly. It is evidently merely a phase of the coarser rock. It occurs both 

 in small imbedded patches (879) and in large, distinct outcrops (905, 903). According 

 to the microscopic examination, those finer kinds, whilst having the same ingredients as 

 the coarser, show a larger proportion of hornblende, and may be designated as " horn- 

 blende rock." Clilorite appears to occur in all, more especially in the finer kinds, as an 

 accessory. 



For the most part the bedding of the Little Bull rocks is indistinct. In two places, 

 however, it is plainly to be seen. One of those is on the west wall of a dry side chan- 

 nel near the head of the main island. Here very marked planes dipping 27° S. W. and 

 striking N. 5° W., are to be seen along a perpendicular exposure, 20 feet in height and 

 60 in length, of the prevailing coarse syenite. Across the bedding lines run a number 

 of jomts bearing N. 42° W., and dipping 87° S. W. The other place, distant from 

 here 800 feet in a nearly due south direction, is on the same island, and on the west side 

 of the east or main channel, just below the dam. Here are a number of distinct layers 

 of the finer grained rook (908), averaging 14 inches in thickness, and dipping 30' E., 

 with a north and south strike. Wo have thus indications of a low anticlinal, whose 

 nearly north and south axis runs diagonally across the island, and nearly in tlie direction 

 of the river above. 



On the large exposm-e mentioned as showing a westward dip, the bedding planes are 

 cut by a vertical north and south vein of fine-grained, dark-colored, brown-weathering, 

 homblendic rock (899), wliich is itself traversed and partly faulted by joints that affect 

 it and the wall rook ahke. Several large, white quartz veins show under the bridge 

 acr'oss the first dry channel west of the main gorge. One of these bears N. 40° B., 

 dips 17° N. W., is five feet wide, and composed of parallel bands a quarter of an inch 

 to three inches in width. A still larger one occurs at the bottom of the gorge, where it 

 stands out very prominently, the smxounding rock Iraving been worn away by the run- 

 ning water. The wall rock, seen in only one place, is fine-grained, schistose, dark- 

 greenish, and apparently chloritic (902). It would seem to bo an advanced stage of al- 

 teration of the normal amphibolic rock of the vicinity. A less advanced alteration is 

 shown by the rock (905) of the large outcrops on the northwest corner of the island. 



The Mosinee hills are two spm-s of an isolated elevation on the west bank of the 

 Wisconsin, m Sees. 27, 26, 25 and 22, T. 28, R. 7 E., Marathon county. They are 

 both of quartzite, and are higher than the rest of the elevated ground around them. 



The Lower Mosinee hiU is near the center of Sec. 27, and about a mile from the river 

 bank. It is conical in shape, with slopes of about 30° near the summit, and rises to an 

 altitude of 880 feet above Lake Michigan, or about 280 feet above the river near by. 

 Its slopes and summit are covered with loose masses of quartzite, one-foot cube to four- 

 feet cube in size. Tliis quartzite (923) or quartz, is greyish-wliite, occasionally stained 

 yellow, vitreous, and translucent in thin pieces, and pecuharly brittle. Sometimes a 

 shght tendency to a granular structure is to be noticed. 



The Upper Mosmoe hiU. is reached from the Lower hill by crossing a saddle between 

 the two. On this saddle, on the N. E. qr. of Sec. 27, numerous more or less rounded 

 fragments of a fine-grainod, reddish felspathic rock occur. The Upper liill is on the 

 S. E. qr. of Sec. 23, near the corner of the section. It reaches an elevation of 1,030 

 feet, or about 430 feet above the adjacent river. Its slopes, like those of the Lower hill, 

 are covered with loose angular fragments of white, vitreous quartz of all sizes, up to five 



