122 GEOLOGY OF ILLINOIS. 



species, on account of the incoherency and fragility of the material. The more 

 solid beds were not rich in fossil remains ; the only specimens found were frag- 

 ments of Calymene senaria, and Lingula. A little over two miles from this 

 point, near the middle of the dividing line between sections 17 and 18, or a 

 little over into section 17, is another quarry into a yellowish, and in some 

 parts reddish, porus limestone, almost entirely made up of undistinguishable 

 organic remains, and containing also some well preserved fossils. The depth of 

 the excavation was about five feet, with apparently no change in the character 

 of the rock. About a quarter of a mile farther south, I observed another 

 similar excavation in similar beds of limestone. 



Mention has been made in the remarks on the Niagara group, of an isolated 

 exposure of Cincinnati beds forming the base of a low anticlinal, cut through 

 by Fox river, in the western part of section 3, township 40, range 8. No good 

 section is afforded at this place, as a sloping, grass-grown talus extends almost 

 uninterruptedly from the foot of the ledges of Niagara limestone to the level 

 strip of bottom land along the river. The highest point to which this forma- 

 tion extends in the axis of disturbance, is about thirty feet above the river. 

 The upper beds here appear to be shaly, containing many thin plates of a highly 

 fossiliferous gray limestone, containing many of the characteristic fossils of this 

 group. These are washed out abundantly in the small runs and water channels 

 in the bank, and afford in great numbers Orthis subquadrata, Ortliis biforata, 

 0. testudinaria, 0. occidentalis, Strophomena alternata, Leptsena sericea, and many 

 other common species. 



Trenton Group. The upper beds of the Galena limestone, which alone are 

 included in the surface outcrops of this district, underlie the surface in that 

 portion of DeKalb county lying west of the area already mentioned as occupied 

 by the Cincinnati group. The exposures are few and, with one exception, con- 

 fined to the banks of the Kishwaukee and its immediate vicinity. The princi- 

 pal exposures are as follows: 



Near the center of the western half of section 30, township 42, range 3, and 

 about a quarter of a mile from the western line of the county, I observed, in a 

 small ravine at the side of the road, a ledge of thinly bedded, buff colored, po- 

 rous, fossiliferous limestone, which had been quarried to some extent, and was 

 exposed in the natural and artificial section to a depth of about ten feet. No 

 dip was perceptible in this exposure. The fossils were, from the nature of the 

 rock, very imperfect, being principally very indistinct internal casts of Mur- 

 chisonia, Pleurotomaria, etc. Similar beds of limestone are said to occur in 

 the bed of the Kishwaukee, in the northern parts of sections 21 and 22, but at 

 the time of my visit the water was too high to make any thorough examina- 

 tion. 



