592 



GEOLOGY OF CENTRAL WISCONSIN. 



bridge of considerable dimensions. The arch is about ten feet thick, its under side being 

 30 feet from the ground, and the width of the archway 30 to 40 feet. The rock is the 

 upper portion of the Potsdam, containing the usual calcareous bands, and is highly 

 charged with small pebbles of red quarfczite. The bases of the cliff's on both sides of the 

 valley of that branch of Honey creek which follows the west line of T. 10, R. 5 E., are 

 made up of a layer 50 feet thick, of whito, non-calcareous sandrock, which is rendered 

 very prominent by its strong contrast in color with the darker hued layers at higher 

 levels. Its upper surface appears to be about 155 feet below the Mendota base, and the 

 layer is evidently the same as seen at the foot of the great bluff at the mouth of Honey 

 creek. 



FIG. 47. 



Slane WU7unJ SJ'*^- '' 

 QG exposure /*/r .il 



I&acl 



^ '--' 



Feet. 



SECTION OP RIVTB BLUFF NOBTH op SPRING 

 Horizontal scale, 235 feet to the inch; vertical scale, 100 feet to the inch. 



The Mendota is quarried on the side of a steep ravine in the river bluffs immediately 

 north of Spring Green, N. W. qr. Sec. 3, T. 8, R. 4 E. The point of the bluff at the 

 mouth of this ravine shows the profile and section as indicated in Fig. 47. The succes- 

 sion of layers, including the quarry across the ravine, is as follows : 



I. Lower Magnesian limestone: in numerous small, rough-weathered expo- 

 sures; upper layers concretionary; about midway of the measurement, 

 close-textured, white, crystalline, with chert and a few dolomite-Lined cav- 

 ities; at 20 feet above base, sandy, and including red quartzite pebbles; 

 lowest layers seen, brownish, concretionary, rough-surfaced, with chert and 

 facings to the layers of stalactitic carbonate; at base a greensand layer; 



exact junction with the next formation seen 



II. Madison sandstone: in perpendicular ledges, including: white, indurated 

 sandstone, with red quartzite pebbles, 13 feet; loose, white, cross-lami- 

 nated sand, 7 feet; unexposed, about 15 feet; in all 



HI. Mendota beds: including: unexposed, about 25 feet; thin, crumbling, lime- 

 stone layers, b% feet; yellow calcareous shale \% feet: seven very regu- 

 lar, heavy, yellow, limestone layers, with a 6 inch parting near the base, 



65 



45 



