14 GEOLOGY OF ILLINOIS. 



range 2 west, there is about twenty-five feet in thickness of this limestone to 

 be seen, dipping south 20 west, at an angle of about 24. This is the most 

 southerly exposure of this rock that has been seen in the county. 



On the west side of the county, on the north line, this limestone forms the 

 upper escarpment of the bluff, and in crossing the county from Eeed's Land- 

 in<* to Bay creek, through the north tier of townships, it forms the bed rock 

 over all the highlands between the two rivers. Following down the Mississippi, 

 it forms almost continuous exposures along the bluffs on the west side of the 

 county, to Hamburg, where the upper escarpment of the bluff is formed in 

 part of this limestone, and in part by the limestones of Kinderhook group. 

 From this point, its outcrop trends eastwardly, and the underlying formations 

 take its place in the river bluffs, but it continues to form the upper portion of 

 the dividing ridge between the two rivers, down to the center of town 12 south, 

 range 2 west, which is its most southerly point of outcrop in the interior of 

 the county, on the north side of the Cap au Ores fault. Below that fault, it 

 is only seen at one point on the west side of the county, where the upturned 

 edges of its nearly vertical strata, constitute the first rock exposure below the 

 Cap au Ores bluff. This exposure is about two hundred yards below the south- 

 ern terminus of the sandstone bluff, and the strata are in a nearly vertical posi- 

 tion, dipping south 20 west, at an angle of at least 60. A measurement 

 across the upturned edges of the strata, indicated a thicknsss of about two 

 hundred feet. The Kinderhook shales and limestones are not exposed here, 

 but probably underlie a part of the valley of the small creek which enters the 

 river at this point. The Keokuk limestone is found immediately succeeding 

 the Burlington here, but with a diminished dip, and it is overlaid by the St. 

 Louis limestone, the upper portion of which holds a nearly horizontal position. 

 The wood cut on page 2 illustrates the position of the various formations seen 

 in connection with this fault, much more clearly than any verbal description 

 that could be given. 



Keokuk Limestone. This division of the Lower Carboniferous series is only 

 met with at the single locality above mentioned in this county. It immedi- 

 ately succeeds the Burlington limestone below the Cap au Ores bluff, and, 

 although the dip is considerably less than that of the underlying limestone, it 

 is nevertheless sufficiently strong to carry all the exposed beds of this group 

 below the surface, in a distance of about one hundred and fifty feet. Its entire 

 thickness here, probably, does not exceed one hundred feet, though an accurate 

 measurement could not well be made here. The upper portion appeared to be 

 shaly, and was filled with the silicious geodes, characteristic of the upper part 

 of this group at more northern localities. The lower portion was composed of 

 gray limestones, similar to the quarry rock at Hamilton and Nauvoo. On the 

 eastern side of the county, it should be found between the outcrop of Burling- 



