DEKALB, KANE AND DUPAGE COUNTIES. 121 



The remaining eight feet exposed, to the bottom of the quarry, represent No. 4. 

 The whole thickness exposed is fourteen feet and five inches. The fossils are 

 similar in species to those collected at the former locality, Pentamerus oblongus, 

 Halt/sites catenularia, and various indeterminate casts of corals and shells. 

 There is, at this locality, a very slight dip to the eastward, not more than one 

 or two degrees. North of this point there are no exposures of the older rocks 

 along the river within the limits of the county. 



The only exposures of the Niagara group which remain to be mentioned as 

 occurring within this district, are met with in the forks of Big Rock creek, in 

 the southern portion of section 26, township 38, range 6, in the southwestern 

 portion of Kane county. There are here two principal outcrops, one on each 

 branch of the stream, and not more than a quarter of a mile apart. The bot- 

 tom land lying between the two, is also underlaid at a depth of from two to four 

 feet by the same rock, which has here been also artificially exposed at a point 

 about midway between them. At the easternmost exposure, the rock is a soft 

 ferruginous limestone, of a yellow, and, in some specimens, reddish color. At 

 the diggings on the western fork, and in the bottom land, it seems less ferru- 

 ginous and more compact and hard, and generally better fitted for use as a 

 building and flagging stone. As nearly as could be made out, the strata were 

 horizontal. The limestones here are hardly fossiliferous ; such few specimens 

 as were obtained, however, were identical with those found near the base of the 

 formation elsewhere. On the creek below this point, no exposures are met 

 with north of Kendall county line, though the rock is evidently not far beneath 

 the surface. 



Cincinnati Group. The rocks of this group underlie a small area in the 

 northern part of DeKalb county. As, however, they are exposed at only two 

 or three points within this area, it cannot be defined with any exactness ; it 

 may, however, be approximately described as a narrow strip, extending into this 

 county from the north or northeast, and having a width from east to west of 

 probably not more than eight or ten miles. Its western border is probably 

 somewhere near the west line of range four of townships east of the third 

 principal meridian. South of the Kishwaukee, or Sycamore river, there are no 

 outcrops in DeKalb county, its limits therefore cannot be well defined in that 

 region, though it probably does not extend very far to the southward. 



One of the few exposures of this group in the DeKalb county area, occurs on 

 the north bank of the Kishwaukee, just north of Stewartsville, where about 

 fifteen feet of interstratified green and blue shales and rotten limestone, with 

 some more solid beds, were seen. The exposure continues only so far as the 

 beds have been worked. Elsewhere the high banks of the creek present only 

 grass-grown slopes. No dip was observed in this locality, nor were any fossils 

 discovered except a few fragments of Trijobites generally ^distinguishable as to 

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