CAttROLL COUNTY. 79 



the Cincinnati shales, but their summits are capped with the Niagara 

 rocks. Like vast mural structures they rise along the highest eleva- 

 tions, weatherworn into all kinds of fantastic shapes now displaying 

 in their escarped cliffs resemblances to old forts and ruined cathedrals, 

 time-worn castellated battlements, or distant spires and minarets of 

 some old town. Such is the appearance of these rocks along the river 

 bluffs above Savanna and towards the southern line of the county. The 

 beholder, especially if he be a geologist, feels a strange spell stealing 

 over him. Mighty visions of the old geologic ages enrapture his soul. 

 A leaf from the old stone book is upturned before him, and he reads in 

 the great Bible of Nature her sublime truths. He has discovered hard 

 . common sense in the rocks. 



But enough of dream and fancy sketching. Leaving the river, we do 

 not find exposures of this limestone. Over the northern and north- 

 western portions of the county, all the highest portions are covered with 

 it, in broken, fragmentary masses. Once it doubtless covered a large 

 part of the county, but it has been denuded and carried off, leaving 

 chert beds, corals and fragments of the rock itself as memorials of 

 where it once existed as the surface rock. The frost, the rain and the 

 atmosphere pulverize the Niagara rocks, and the chert beds in them 

 being harder, settle down, like a crop of white flints sown over farm, 

 field and hill. These chert beds show that the water of the old Niagara 

 seas contained much silica in solution. 



The Niagara Limestone abounds in fossils. The most common and 

 characteristic is the beautiful Pentamerus oblongus, or " petrified hick- 

 ory nuts " of the miners. But the old Niagara seas were particularly 

 the homes of the coral builders, and these minute animals swarmed in 

 countless myriads everywhere, leaving their fossil monuments. Among 

 the most characteristic are the Favorites farosa, F. lfiagaresi ; 

 Stromatopora coneentrica. Halysites catenulatus, and many other species 

 and genera, containing, doubtless, new and undescribed corals. 



This brings us through the Illinois rocks as developed in this county. 

 Sometimes traces of the Trenton proper are found in the southern part, 

 but they hardly deserve a place in the surface geology of Carroll county. 



The rocks of all three of these formations possess value as building 

 stone. The Galena ranks first, and the Cincinnati group last in econ- 

 omic value. 



THE QUATERNARY SYSTEM. A llur i urn. The Mississippi bottom, 

 from Savanna to the south line of the county, in width averaging nearly 

 five miles, is composed of this recent river deposit. The same deposit 

 also exists north of Savanna, on the Mississippi, and along some of the 

 small streams in the interior. Some of it is a rich, deep, black and 



