CARROLL COUNTY. 77 



county, although it is reached in sinking deep wells in the .south-eastern 

 part ; and one quarry of the real blue Trenton limestone is now worked 

 in Ogle county, two or three miles Irom the county line. 



Of the characteristic fossils, the JReceptaculites Sulcata, or " sunflower 

 coraF of the miners, is the most usually observed, and very perfect spe- 

 cimens are sometimes found. The Murchisonia obtusa and Lingula 

 quadrata also abound. Orfhocera, several feet long; several species of 

 the Orthis; corals of a number of species also abound. A very inter- 

 esting species of trilobite has left its remains in these rocks ; and we 

 firmly believe that many new fossils will be found, when the quarries in 

 tliis rock are carefully and scientifically examined. Of the economic 

 value of this rock we will speak again. It is the underlying rock in 

 perhaps two-thirds of the county, embracing the central, northern and 

 eastern parts, being our chief building stone. 



The Cincinnati Group. The gentle slopes from the Mississippi bot- 

 tom lands up to where the bluffs are capped with the castellated crags 

 of the Niagara rocks, if exposed, would reveal outcrops of this group. 

 Some of the smalt streams have cut down into this formation through 

 the overlying Niagara. Johnson creek, winding in a sinuous course 

 from the central to the south-western portion of the county, shows the 

 same rocks, sometimes near the surface. One-half of the southern part 

 of the county has this as the immediate underlying formation. About 

 one mile bflow Savanna there is a fine outcrop, where the county road 

 cuts the side of the hills. About one mile above Savanna there are 

 considerable quarries opened in this formation, on the side of the bluffs. 

 Here the formation, as near as we can measure, is 80 feet thick. This 

 is the best place in the county to make a section. At some large springs, 

 just at the level of the Mississippi, in a full stage of water, the group 

 begins, resting solidly on the Galena limestone as a foundation. Far 

 up the hillside, the overlying Niagara rocks are just as distinctly 

 marked. In the railroad cut, on the Tomlinson farm, some four miles 

 south-west of Mt. Carroll, may be found another, and perhaps the finest 

 exposure in the county. At Bluffville. also, it is exposed by quarries. 

 There are, however, few natural exposures of this rock. It soon disin- 

 tegrates and crumbles away. Gentle hills and slopes, and graceful un- 

 dulations are characteristic of its physical geography. Many springs 

 burst out from the bases of these hills, and marshes and swampy places 

 are not unfiequent. Shales and shaly limestones compose a large part 

 of the rocks of this group : but its lower beds are sometimes solid and 

 massive enough for a building stone, and even contain lead in small 

 quantities. These shales are of a bluish-white color. Their particles 

 are finely comminuted, as if deposited in deep, peaceful seas. 



