THE LOWER SILURIAN ROCKS. 579 



(1416), aiternating with flner-grained, more friable layers (1415). The coarser irock ia 

 the most calcareous, consisting of miloh-roUed grains of dulled quartz, with 30 per cent. 

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

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

 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, hght brownish, very fine-grained, firm, non-calcareous- 

 sandstone (.14141^) is exposed. With the exception of Mt. Morris, tlie hrae bluflfs of north- 

 western Marquette county, and a few points m 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 foet below the Mendota, and in general 200 to 300 feet. 

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

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

 been very ccfnsiderable, the lacustrine clays reaching a tliickness 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-eiglit 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. Morris, as 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 tliis 

 place, could hardly be less than 650 feet. 



Very good, hard, white sanc^ock 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 Kapids 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. Tlie quanry 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 jomts 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, the 

 whole quarry face bemg much iron-stamed by weathering. The heavy layers below, 

 however, present a very much mduratcd, nearly white, fine-gramed sandrock (760), 

 made up of grams of sharply angular, gla.ssy quartz, and obtainable in veiy large^ 

 straight-edged, smooth-faced blocks, wliioh dress readily. The rook is a quite unusually 

 good building material. 



Satik and Columbia Ccttnties. 



(Atlas Plates XIII and XIV, Areas D and E.) 



Those portions of Sauk county lying west of the west line of R. 4 E., ai-e not here m- 

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

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

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

 the Wisconsin, oversteps the Umits of the rectangle, adding three enture townships and 

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

 is 1351.5 square miles, including 785 square miles for Columbia, and 566 5 square 

 miles fortliat portion of Sauk county liere described, the whole of Sauk county havmg 

 ■ an area of 796.5 square miles. 



