28 GEOLOGY OF ILLINOIS. 



Sandy shales ' 38 



Blue clay shales 44 



Covered slope to the level of the road 2*7 



Probably about fifteen feet in thickness at the base of this section, is occu- 

 pied by the Niagara limestone, leaving 120 feet as the aggregate thickness of 

 the Kinderhook group at this point. The sections above given will illustrate 

 the general character of this group, as it appears in this county, where it is 

 composed mainly of sandy and argillaceous shales, with some thin beds of lime- 

 stone. Its outcrop is confined to the river bluffs, and the lower courses of the 

 small streams that intersect them. Commencing on the west side of the coun- 

 ty at the north line, we find from forty to fifty feet of these shales outcropping 

 below the Burlington limestone, which forms the upper escarpment of the bluffs, 

 and thence southward they gradually rise until, at Rockport, we find the whole 

 thickness of the group in partial exposures above the level of the bottom road. 

 In the vicinity of Pleasant Hill, the bluffs are composed of Niagara limestone, 

 overlaid by Loess and Drift, and the outcrop of the Kinderhook is found further 

 back on Six Mile creek and on the branches of Bay creek. On Cold Run, 

 about a mile above the point where it enters Bay creek, the green and blue 

 shales of the Kinderhook group are well exposed, giving a measured section 31 

 feet in thickness. These are overlaid by sandy shales, that are but partially 

 exposed, but containing a few feet in thickness of fine grained, evenly bedded 

 sandstone, that has come into general use in the neighborhood for constructing 

 chimneys, building foundation walls, etc. It is said to be a very refractory 

 stone, that is scarcely affected by the action of fire, and also possesses a fine, 

 sharp grit, which makes it a useful material for grindstones, whetstones, etc., 

 for which it has been very generally used in this vicinity. The bed, however, 

 is only from three to four feet in thickness at the point where we found it ex- 

 posed, which was about three-quarters of a mile east of Mr. J. Gr. Sitton's farm.* 

 These beds, and the blue and green shales which underlie them, will be found 

 outcropping on all the tributaries of Bay creek, in this vicinity, as well as on 

 the main creek. 



Crossing the county to the Illinois river bluffs, near the south line, we find 

 these beds forming the lower portion of the bluff, and well exposed on the 

 lower course of Bee creek, and in the bed of the creek at the mill, there is a 

 partial outcrop of the black shale, which sometimes forms the lowest strata of 

 the group. The beds are not fully exposed here, but in ascending the stream, 

 the argillaceous and sandy shales are occasionally seen in partial exposures, 

 showing that the group retains essentially the same characters on this side of 



*A rock exactly like this, from Marshalltown, Iowa, and from the same geological horizon, 

 receives a high polish, and is used for tables and various other purposes, as an ornamental 

 stone, and the rock from the above named locality, in Pike county, seems to be equally as well 

 adapted for this purpose. 



