THE LOWER SILURIAN ROCKS. 



585 



"fel 



^ 



g: 



Fig. 38 is a section from south to north along tlie center line of 

 Sees. 2, 11, 23 and 26, in Uie town of Scott, T. 13, R. 11 E., and 

 serves to give a correct idea of the topography and stratigraphy 

 of that township. 



Large ledges of Potsdam sandstone rise on the south side of a 

 small creek in the N. E, qr. of the N. E. qr. of Sec. 3, Arling- 

 ton, T. 10, R. 9 E., a short distance south of the village of 

 Poynette. Here are exposed 15 feet of white, heavily-bedded, 

 friable, non-calcareous sandstone, with some tliiu gxeensand lay- 

 ers, the base of the ledge beuig 60 to 80 feet below the base of 

 the Mendota horizon. Similar but higher ledges occur along 

 the creek in Pine Hollow, in the adjoining parts of Sees. 3 and 4. 

 The St. Peters sandstone remains on top of the Arlington prai- 

 rie in five isolated knobs, the highest 70 to 100 feet in height, 

 lliree of these are close together on each side of the line between 

 Sees. 28 and 29. The bluff on Spoonam's land, N. E. qr. of the 

 S. E. qr. of Sec. 29, shows large outcrops, in a disturbed condition, 

 of fine-grained, friable, white-and-brown-mottled sandstone (725, 

 . 726), composed of glassy quartz grains, the larger ones of which 

 g are rolled, the smaller ones angnlar. Most of the rock is affected 

 ^ by a very hard, vitrified crust, }4 ^ % inch in thicloiess, in 

 n which the quartz grains appear to possess distinct crystaUine sur- 

 ^ faces. No trace of calcareous matter is present. Fine-lamina- 

 ^ tJon and cross-lamination are plainly perceptible. The knob on 

 S Mrs. A. D. Forbes' land has on the south side a vertical chff, 80 

 S feet in height, of similar but distinctly horizontal and undisturbed 

 i sandstone. In the S.'W. qr. of the S. W. qr. of Sec. 27, and ex- 

 I tending into Sec. 28, and again in the N. ht. of Sec. 34, are other 

 % similar bluffs. On the prairie around these sandstone mounds, 

 ^ exposures of the Lower Magnesian hmestone are seen at several 

 points whose elevation is greater than that of the base of the 

 sandstone ledges, wliilst at least two points, on the south line of 

 Sec. 21 and in the north part of Sec. 29, show the Hmestone ris- 

 ing as high as the top of the St. Peters. The in-egular nature of 

 tl\e upper surface of the Lower Magnesian is thus distinctly 

 proven. 



In Fort Winnebago, T. 13, R. 9 E., the'only formation is the 

 Potsdam sandstone, which, in the middle and western portions, 

 and again in the southeast, rises in isolated bluffs. At T. Cough- 

 lin's quarry, N. E. qr. of S. W. qr. Sec. 20, ai-e exposed 10 feet 

 of heavily-bedded, fine-grained, white, porous, friable sandstone 

 (741), which is composed of glassy, sub- angular, quart? grams, 

 and is blotched with fen-uginous spots. Rows of little brown- 

 stained pores mark the lammation very plainly. Large fucoidal 

 impressions occur, identified by Mr. Whitfield as Palceophyms 

 duplex, and Palwochoida, n. sp. Large regular shaped blocks are 

 obtained. The isolated bluff on the adjoining parts of Sees. 25 

 and 36 shows numerous small exposures of white, crumbUng, 

 non-calcareous sandstone, for a thickness of about 90 feet. Fig. 39 is a section from 

 this bluff across the Wisconsin at Portage to flie quartzite bluffs of Caledonia. The 

 contomr of the section is copied from Gen. G. K. Warren's report on the Fox and Wis- 

 consin rivers. 



