CALHOUN COUNTY. 7 



The Niagara limestone extends below the river level, at all the exposures in 

 the vicinity of Hamburg, and its entire thickness is not seen. On the north- 

 west quarter of section 19, township 10 south, range 2 west, the rock was 

 quarried for the jail at Hardin. At the base of this formation here, where it 

 rests on the blue clays of the Cincinnati group, we find from two to four feet of 

 light gray oolitic limestone forming the lower beds, which are overlaid by the buff 

 and brown dolornitic limestones in which the quarries for building-stone were 

 opened. These beds are here about fifty feet in thickness, and probably comprise 

 nearly the whole thickness of the Niagara group at this point, for on the adjoin- 

 ing section, on the small creek which intersects the bluffs on section 18, township 

 10 south, range 2 west, the Hamilton limestone is found in place overlying the 

 Upper Silurian strata. 



From this point south, to a point a mile below Grilead, these limestones con- 

 tinue to show themselves in occasional outcrops, forming the upper portion of the 

 bluff, while below, there is a sloping talus, underlaid by the blue argillaceous 

 clays of the Cincinnati group. Below Gilead, the line of outcrop of the Niag- 

 ara limestone, and overlying formation recedes from the river bluffs, and is 

 found in the hills from one to two miles back, towards the interior of the 

 county. It continues in a southerly direction to section 28, township 12 south, 

 range 2 west, where its trend is changed to the eastward across the county, by 

 the disturbing influences that caused the Gap au Ores fault. 



Its most southerly outcrop on the eastern side of the county, is in the vicinity 

 of the Stone Church, two miles below Monterey, where about twenty feet in 

 thickness of buff limestone is exposed, and has been quarried for building-stone 

 in this neigborhood. Between this point and Monterey this limestone is mostly 

 hidden under the overlying Lower Carboniferous formations. At Mr. C. W. 

 Twitchell's place on the southeast quarter of section 10, township 12 south, 

 range 2 west, this limestone has been quarried, where it forms a precipitous 

 bluff some forty to fifty feet high. 



At the point of the bluff above Monterey on the Hardin road, on the north, 

 east quarter of section 11, in the same township, the following measured sec- 

 tion was obtained: 



FT. 



Hamilton limestone : 12 



Buff colored Niagara limestones 50 



Covered slope with partial outcrops of blue clays 48 



The blue clays forming the lower part of this section undoubtedly belong to 

 the Cincinnati group, and, though the junction of the Upper and Lower Silu- 

 rian strata could not be seen here, it is probable that nearly the full thickness of 

 the Niagara limestone is represented in the above section, as this is about its aver- 

 age in this part of the county. From this point northward along the bluffs of the 

 Illinois river, the brown and buff limestones of this group continue, in occa- 



