564 GEOLOGY OF CENTRAL WISCONSIN. 



however, occur, caxrying its thickness up into the hundreds of feet, and bearing witness 

 to the great thickness which once must h<iye existed over all the region. 



In Sec. 23, T. 21, R. 8 E., Portage county, on the edge of the great Plover marsh, 

 rises a jirominent knob of sandstone, known as Mosquito Moiinf ain. The bluff is about 

 100 feet high, with its main extent east and west. Just west of it, on the west side of 

 the Portage jtnd Stevens Point road, is a second lower knob. Near the base of the main 

 hiU, the sandstone, as seen in a quarry (789), is rather tme-grained and Hght-colored, with 

 brownish spots and laminEe, and very friable indeed. It is composed of grains of limpid 

 quartz, that are all somewhat rohed, but are still subangular in shape, and has a very 

 minute quantity of a brownish cement. Tlie bedding here is very distinct, the layers 

 running from 2 inches to 1 foot in tliickness on a quarry face of 15 feet. One hundred 

 yards to the east of the quarry, on the same hfll, are ledges of a much coarser and more m- 

 durated sandstone (790), which is in places almost Hke quartzite, having a whitish color, 

 and composed of much-rolled grains of vitreous quartz, closely cemented. A similar rook 

 (791) occurs in small exposures up to the summit of the ))Iuff. On the western bluflf a 

 quarry exposes coarse-grained, brownish, moderately finn sandstone (792), having a 

 semi-vitrified appearance on the exterior. 



At the foot of Conanf s Rapids, S. E. corner Sec. 8, T. 23, R. 8 E., 3D feet of hor- 

 izontally bedded sandstone show in the river bank, o verlj'u ig gneiss. The lowest layers, 

 in contact with the gneiss, are hard and quartzite-Uke; but the body of the exposure is 

 thinly bedded, coarse-gra,ined, friable, and of a light-brownish color. 



At Steven's Point, just below the railroad bridge, on tlie east bank of the river 

 (Plate IX, of I'ig. 12), thin-bedded friable sandstone shows at the top of the bank, the 

 gneiss being exposed below. 



On the west side of the river. Sec. 31, T. 24, R. 8 E., is a low outlier of sajidstone, 

 rising 51 feet above the river. The sandstone is cut into deeply at the south end of tlio 

 mound, for the railroad, and this cutting is expanded into a quarry at one point. 

 , Another large quarry is worked on the northwest side of the hill. In the cutting, the 

 upper layers are thin-bedded, whilst the lower seven feet is in heavy layers, and shows 

 a hght brownish, white, much indurated, rock (774), of a medium grain, and composed 

 of highly glassy, subangular,- quartz grains. Fresh surfaces are quite uniform in ap- 

 pearance; weathered surfaces much iron-stained. Strong joints occur trending N. 15° 

 W. and N 50° E. Pieces 4 by 4 by 4 J^ feet can be obtained easily, also thin slabs fit 

 for flagging. The quarry on the west side of the hiU shows a similar stone, taken from 

 higher layers. Tlie topmost layer in the quarry is very beautifully ripple- marked. The 

 stone from these quarries is a valuable one, and is much used in building at Stevens Point. 



About four miles north of Grand Rapids, in the town of Rudolph, S. E. qr. Sec. 20, T. 

 23, R. 6 E., Wood county, a large and excellent sandstone quarry has been opened near 

 the summit of the ridge, whose slope for half a mile southward shows sandstone ledges. 

 The quarry face is 20' feet, and shows very plainly bedded layei-s 1 inch to 2 feet in 

 thickness. These are traversed by very strong joints, trending N. 10° W. and N. 70° 

 to 80° E. Some of the joints are inclined, especially the former set, most of which dip 67° 

 W., and others are vertical. All the stone is tolerably firm, but most of it is not unusually 

 indurated, crumbling easily in the fingers. Cert,ain layers, however, are very liighly in- 

 durated, and are susceptible of quite a liigh polish. These are both plain white and 

 wliite heavily streaked with dark red, are of a rather fine grain, and consist of sub- 

 angular grains of highly vitreous quartz. Large blocks can be obtained, as also thin 

 flags 10 by 18 feet. The stone is much used at Grand Rapids, and has a considerable 

 value. 



Along the Wisconsin river, from Grand Rapids to Point Bass, sandstone is fre- 

 quently exposed. Several sections in the vicmity of Grand Rapids, shovring sandstone 

 overlying kaohn, have already been described. 



