140 GEOLOGY OF ILLINOIS. 



bling true chert in appearance, and breaking with its conchoidal fracture. 

 Farther up the ravine, we find above this, six or seven feet of a rather darker 

 colored, thin bedded limestone exposed. No fossils were obtained from any of 

 the beds in this locality. 



Across the river from this point, there is a rather more extensive quarry in 

 apparently the same bed of limestone, which is worked, both for building stone* 

 and for material for the manufacture of lime. 



In the village of Oswego, in a perpendicular face of rock on the bank of 

 Waubansia creek, a few rods below the bridge, about five feet of the low- 

 ermost beds of the Niagara limestone may be seen, resting directly upon the 

 strata of the Cincinnati group. The rock here is a brownish, ferruginous lime- 

 stone, and contains a few fossils, chiefly corals, Stromatopora concentrica, and a 

 Zaphrentis, being most abundant. Thin seams of chert traverse the rock here, 

 as in the other localities. The dip of the strata here is to the eastward, about 

 three or four degrees, thus bringing to view a greater thickness of these beds 

 further up the stream. A little above the bridge, near the lime kiln, and still 

 farther up, there cannot be less than twenty feet in exposed vertical thickness, 

 of the Niagara limestone, in the sides of the ravine. 



The only remaining exposure of rocks of Niagara age in this county, is on 

 Waubansia creek, in the northern part of section 16, a little over a mile from 

 Oswego. At this point, the rock underlies the prairie at a very slight depth, 

 over an area, probably, of several acres, and is exposed in the bed of the creek, 

 and in the artificial excavations of the quarries. This exposure is of a light 

 buff or drab, thin bedded limestone, containing some shaly layers. It also con- 

 tains, in some of the upper layers, many small nodules of iron pyrites. The 

 whole depth of the excavations in the rock at this place, was not more than 

 four feet at the time of my visit, and for this reason I could not compare this 

 exposure with some others in this county, as satisfactorily as I could wish, but 

 I consider it as higher in the formation than any of them, probably fifty feet or 

 more above the base. 



Fossils were neither abundant or well preserved at this locality ; a few frag- 

 ments of Trilobites and corals only, were collected. 



Cincinnati Group This formation occupies a considerable area, lying south 

 and west of that underlaid by the Niagara group, equal, perhaps, in extent to 

 one-third of the whole superficial area of the county. Its western border would, 

 perhaps, be nearly represented by a line running from north, northwest to 

 south, southeast, and crossing the Fox river in the southeast quarter of section 

 35, township 37, range 6. The line of junction between it and the formation 

 next below, is not shown anywhere in Kendall county. 



The upper beds of this formation are well exposed at Oswego, directly under- 

 lying the lowermost strata of the Niagara group . The following section of these 



