ROCK ISLAND COUNTY. 227 



almost to the southern line of the county, except in a few places, where 

 an uncultivated, low bottom intervenes, seamed with running sloughs. 

 This range of bluffs is cut up with hollows and ravines; is covered with 

 a moderate growth of timber, principally the oaks ; the rough land, ex- 

 tending back into the highlands from two to five or six miles, has a 

 thin, white soil, such as is found in the timber barrens of other portions 

 of the State, and is altogether the least valuable portion of the county 

 for agricultural purp- 



Geolo gical Formations. 



The geological formations consist of the drift clays and usual super- 

 ficial deposits, the Coal Measures, including productive coal seams and 

 dated -Lai. >. -andstones and limestones, and the Hamilton lime- 

 stones. 



I If Hamilton Group. The floor of Rock river from Cauiden almost 

 to the Mississippi is composed of this rock. These massive paving 

 stows as seen in the bottom of the river are irregular in size and con- 

 tour, but are all worn smooth by the ceaseless flow of the strong, swift- 

 run nin g river. Their thickness at this place is unknown ; the massive 

 solidity, conchoidal fracture, and white dove color of the stone, indicate 

 that it belongs to the lower part of the formation. At Lear's new mill, 

 almost in the bed of Rock river, the workmen quarried into the solid 

 stone floor of the river fifteen or twenty feet, with no signs of the bot- 

 tom. Rock river runs over the same rocky floor of Hamilton limestone 

 at and below Cleveland, near the eastern line of Rock Island county ; 

 also at its confluence with the Mississippi, below Cauiden. Between 

 these points the river bottom shows a mud deposit, under which this 

 same formation still probably might be found. Few fossils are found 

 in the rock quarried from this river floor, either in Rock river or in the 

 Rock Island rapids of the Mississippi. 



The Mississippi river has a similar rocky floor from Port Byron al- 

 most to Muscatine. Horse-backs, hog-backs, and great rocky chains, 

 characterize the rapids proper, but the lower part, from Rock Island 

 city down, shows alternating stretches of mud, sand and rocky bottom. 

 At some of the latter places navigation is rendered difficult at low stages 

 of water. The Mississippi river bed from Rock Island to a few miles 

 below Andalusia is composed of the lower member of the Hamilton 

 group, being the same as the floor of Rock river at Cainden. At Aii- 

 dulasia, in the edge of one of the Mississippi sloughs, just between 

 high and low water mark, an excellent stone quarry is opened in this 

 formation. The character of the stone quarried indicate that the 

 quarry is opened in the upper division of the formation. The layers 



