146 GEOLOGY OF ILLINOIS. 



higher undulations of the prairie, and has been quarried for building purposes 

 to the depth of about six feet. It is an unevenly bedded, porous, yellowish or 

 buff limestone, very similar to that, described on the Fox river at Post's mills, 

 and like that, contains very few good fossils. The strata here appeared to be 

 nearly or quite horizontal. 



A little more than a mile and a half east of Lisbon village, in the northeast 

 quarter of section 29, the same beds have been again quarried, on the land of 

 Mr. S. Peterson. About half a mile south of this quarry, on the banks of a 

 small run, I noticed many freshly quarried fragments, which had been taken 

 out of its bed, but the strata in place were not visible at the time of my visit. 

 The stone was similar in all respects to that already described, but was alto- 

 gether richer in organic remains, containing very many epecimens of Receptacu- 

 lites, Zaphrentis, Orthis testudinaria, and various other fossils. Still farther 

 down the course of the same run, in the northeast corner of section thirty-two, 

 just below the crossing of the county road, I saw low ledges of thin bedded 

 yellow or buff limestone, extending for a few rods in the banks of the stream. 



East of these localities, no beds of rock appear above the surface of the 

 prairie, for between two and three miles, though it is evidently not buried very 

 deeply. The nearest exposure in this direction north of the county line, is 

 nearly in the center of the northern part of section thirty-five, on the land of 

 Mr. Lewis Sherrill, who has opened a quarry for building stone at this point 

 The rock is the same as at the localities farther west. Though not perceptible 

 to the eye, the rocks here have a slight dip to the eastward, not more, probably, 

 than twenty or thirty feet in a mile. The most eastern point where the rock 

 appears at the surface, is half a mile east of Mr. Sherrill's, in a small ravine in 

 the northeast quarter of section thirty-five, and the southeast quarter of sec- 

 tion twenty-six. Still farther east, it has only been struck in wells. 



St. Peters Sandstone. From observations made in the adjoining parts of 

 LaSalle county, it seems probable that a small area in the western part of town- 

 ship 35, range 6, is underlaid by this formation. The tract thus underlaid is 

 of very inconsiderable extent, at most, probably not more than one or two 

 square miles, and includes portions of sections eighteen, nineteen and thirty, in 

 the western part of the township. The only exposures of this sandstone in 

 the county, are those which have been incidentally mentioned in the remarks 

 on the Trenton group, in the preceding pages, as occurring along the Fox river 

 In the center of the southern part of section 19, township 36, range 6, on the 

 western bank of the river, the principal one of these exposures occurs, the sand- 

 stone being brought up by an anticlinal, forming the base of the arch, and is 

 exposed in excavations in the side of the bluff for thirty feet or more above 

 the water. It is here as elsewhere in this part of the State, a soft incoherent 

 mass of white sand, hardly deserving the name of sandstone, so soft, indeed, as 



