THE LOWER SILURIAN ROCKS. 579 



(1416), alternating with finer-grained, more friable layers (1415). The coarser rock is 

 the most calcareous, consisting of much-rolled grains of dulled quartz, with 30 per cent, 

 of yellow-stained, cleavable calcite (and dolomite?) grains, and dark, smooth-surfaced 

 grains of greensand. The horizon is probably within 25 feet of the Mendota, and is 

 from 600 to 650 feet above Lake Michigan. On the N. W. qr. of Sec. 16, 260 feet below 

 the rock on top of the mount, light brownish, very fine-grained, firm, non-calcareous- 

 sandstone (1414%) is exposed. With the exception of Mt. Morris, the lime bluffs of north- 

 western Marquette county, and a few points in the town of Buffalo, Marquette county, 

 the whole region appears to be eroded well down into the Potsdam series, probably 

 everywhere as much as 100 feet below the Mendota, and in general 200 to 300 feet. 

 Even in the eastern towns of Waushara, just east of which, in Winnebago county, the 

 Lower Magnesian is well down into the low ground, the erosion into the Potsdam has 

 been very considerable, the lacustrine clays reaching a thickness of over 100 feet. At 

 the limestone bluff on Sec. 7, T. 17, R. 8 E., Marquette county, the base of the Lower 

 Magnesian is 700 feet above Lake Michigan. Thirty-eight miles from here, in a N. 10 

 E. direction, on Sec. 27, T. 19, R. 14 E., Winnebago county, the same horizon is at an 

 altitude of about 200 feet. The total eastward descent thus shown is 500 feet, or about 

 13 feet to the mile. This descent is, however, by no means uniform, being very much 

 greater in the eastern half of the distance, for the place of the base of the Lower Mag- 

 nesian at Mt. Moms, ad indicated by barometrical observations, is not less than 700 feet 

 above Lake Michigan. These observations were far from any known point of altitude, 

 but allowing all chances for error, the altitude of the Lower Magnesian base, at this 

 place, could hardly be less than 650 feet. 



Very good, hard, white sandrock is quarried about 3 miles from Wautoma, in the 

 town of Mount Morris, Waushara county; at a point about the same distance north of 

 Montello, Marquette county; and again near the village of Packwaukee, in the latter 

 county. The stone from all resembles somewhat the sandstone from the Stevens Point, 

 Grand Rapids and Black River Falls quarries, and may be at the same horizon. The 

 Packwaukee quarry is opened in the top of a low ridge, on the edge of the Fox river 

 marsh, and a short distance from the shore of Lake Buffalo, N. E. qr. of Sec. 30, T. 15, 

 R. 9 E. The quarry face is 15 feet high, and the rock very regularly bedded in layers 

 from 2 inches to 30 inches in thickness, the heavy layers occurring below, the thin ones 

 at top. Strong, smooth-faced joints intersect the layers, trending N. 75 W., N. 35 

 W., N. 17 W., and N. 14 E. The top layers are somewhat soft and brownish, tho 

 whole quarry face being much iron-stained by weathering. The heavy layers below, 

 however, present a very much indurated, nearly white, fine-grained sandrock (760), 

 made up of grains of sharply angular, glassy quartz, and obtainable in very large 

 straight-edged, smooth-faced blocks, which dress readily. The rock is a quite unusually 

 good building material. 



SAUK AND COLUMBIA COUNTIES. 



(ATLAS PLATES XIII AND XIV, AREAS D AND E.) 



Those portions of Sauk county lying west of the west line of R. 4 E., are not here in- 

 cluded. The remainder of this county, and Columbia, constitute a nearly rectangular 

 area, 54 miles from east to west and 24 from north to south, lying just midway between 

 Lake Michigan and the Mississippi river. Sauk county, in its southern portion, along 

 the Wisconsin, oversteps the Limits of the rectangle, adding three entire townships and 

 parts of three others. The whole area of the district, as given by the land-office plats, 

 is 1,351.5 square miles, including 785 square miles for Columbia, and 566.5 square 

 miles for that portion of Sauk county here described, the whole of Sauk county having 

 an area of 796.5 square miles. 



