GEOLOGICAL FORMATIONS. 



677 



sandstone, about 250 feet higher than the stream which flows along 

 their base. 



(3) Pine Knob, on Otter creek, S. E. qr. Sec. 9, T. 7, E. 2 E. 



(4) Pompey's Pillar, S. E. cor. Sec. 13, T. 7, R. 1 E. This is one 

 of the most picturesque and precipitous of all. 



The peculiarity of the hardness of the upper beds has proved of 

 great assistance in tracing the outlines of the formation, in determin- 

 ing its thickness, and detecting irregularities in the surface contour. 



Ripple-marks on the sandstone were only found at one locality. It is 

 at a quarry in the S. W. qr. of Sec. 3, T. 2, E. 5 E., at the grist-mill 

 near the mouth of Whiteside's creek; the top of the sandstone being 

 about 25 feet above the water. The sandstone is very irregularly 

 bedded in thin layers, with many cross lines of deposition, and the 

 upper beds contain many hollow concretions of iron and sand. The 

 ripple-marks were very plainly seen on some of the layers by the side 

 of the road, and were very regular, parallel and well-defined. 



The St. Peters sandstone differs very much in its thickness in dif- 

 ferent localities,^ although this does not appear to be the case so much 

 in the Lead region as near the northern outcrop of the formation, where 

 it is in some places as thin as 40 feet, and in others, not more than a 

 mile or two distant, it is 100, or even 150, feet thick, and seemingly 

 depends on the varying thickness of the underlying Lower Magnesian 

 limestone. The layers consist of subordinate parts of very various 

 lamination, dipping in various directions. 



Many instances were seen of the varying thickness of Lower Mag- 

 nesian and St. Peters sandstone,'* from which the following are se- 

 lected : 



(1) In the S. E. qr. of Sec 26, T. 8, E. 1 E., is a dry run in which 

 the Potsdam is seen in outcropping cliffs; passing above the top of 

 this, a clay soil sets in, which indicates the place of the Lower Mag- 

 nesian, although it is not seen. ISText the St. Peters is seen in bold 

 cliffs 120 feet high; the distance from the lower bed of the St. 

 Peters to the top of the Potsdam being nowhere over 100 feet. 



(2) In the S. W. qr. of Sec. 13, T. 7, E. 4 W., the St. Peters has a 

 thickness of 150 feet, of which the upper 15 feet consist of a soft, 

 white, friable sand, in which the usual concretions and impregnations 

 of iron are wanting. This is underlaid by 20 feet of yellow sand- 

 stone, and this again by a very dark red sandstone. 



(3) In the IS". E. qr. of Sec. 29, T. 8, E. 2 W., the Lower Magnes- 

 ian limestone is just 100 feet thick, and the St. Peters sandstone 

 150 feet. 



' See page 673. ' See page 673. 



