THE LOWER- SILURIAN ROCKS. 593 



and capable of being spHt into thin slabs (1292) 10^ feet; unexposed 10 

 teet; brownish, red stained, porous limestone, 2 feet; in all about 45 



IV. Potsdam sandstoue: including: greensand layer, 1 foot; unexposed, 20 

 feet; white loose sand with brownish greensand, bearing calcareous bands 

 (1290), in a perpendicular escarpment, 5 feet; slope to foot of bluff covered 

 with sand, 84 feet; in all about 2 jn 



Height of bluff — 



Altitude of summit , ,„,. 



• 466 



West of the western end of the quartzite ranges. The sandstone lying at high levels 

 about the quartzite, in the eastern part of the town of Westfleld, T. 1 1 , R. 4 E. , is, without 

 doubt, both in and above the horizon of the Lower Magnesian hmestonc, as indicated 

 by the exposures of that rock to the westward. Half a mile south of the Mendota 

 quarry, on the point of the ridge in tlie E. hf. of Sec. 10, the road crossing the same 



Fig. 48. 



Map and Section SnowiNe the Rblativb Positions or Eikt's Limestone, and the Subeound- 



ING Book Exposures. 



Horizontfd scale 2 miles to 1 Incli. Vertical scale 400 feet to 1 inch. A B C D, line of section. 



ridge eastward is -cut into brown, friable sandstone, having the proper position and 

 cliaracter for the Madison beds. Continuing eastward, the road rises, the ground be- 

 coming fuU of the cherts characteristic of the Lower Magnesian, but on the soutlieast 

 comer of Sec. 10, non-calcareous, indurated sandstone is again in place, at an elevation 

 Wis. Sub. — 38 



