228 GEOLOGY OF ILLINOIS. 



are not so massive as those found in the river ; some of them are of a 

 dove, and even light blue color, and fossils are abundant. Some large, 

 thin slabs of flagging stone lying at this quarry were beautifully mark- 

 ed over the surface with groups and clusters of white encrinite steins, 

 partially weathered out but firmly imbedded in the stone. At new Buf- 

 falo, the opposite steamboat landing, in Iowa, a similar stone quarry is 

 extensively worked. Some of the pieces of stone thrown out of the 

 bottom of these quarries presented a milky-white, and faintly bluish 

 clouded color, and smooth conchoidal fracture: very unusual in stone 

 thrown roughly from the quarry. The middle division of this form- 

 ation, which outcrops between Moline and Rock Island in several 

 places, was not observed south of Eock river. At the latter localities 

 the color is a dirty-brown; the strata thin and broken up ; many thin, 

 shelly layers run through the mass, which disintegrate on exposure to 

 the weather, leaving in the shaly clay thus formed a great abundance 

 of fossil shells and corals. The little spring run, extending up from the 

 stone quarry at Andalusia towards the residence of Dr. Bowman, runs 

 over the top of the Hamilton limestone until it rises into the Coal Meas- 

 ures of the adjoining bluffs. In this little ravine finely preserved fossil 

 shells and many cup-shaped corals may be obtained. 



While speaking of the Hamilton group of this county and its develop- 

 ment along the upper rapids of the Mississippi river, it might seem 

 appropriate to notice the great amount of work now being done be- 

 tween Rock Island and Port Byron by the Government in the bed of 

 the river, and to inquire as to its probable effect upon the depth of 

 water in the Upper Mississippi. Large coffer dams are built in the 

 stream, and a heavy force is employed at low stages of water in drill- 

 ing, chiseling and blasting the rocky obstructions in the steamboat 

 channel, and removing them. Steam and the best improved machinery 

 are freely employed, and the work is making rapid progress. Some 

 rivermen fear the effects of any deepening of the channel upon the 

 supply of water above. This fear in all probability is ungrounded. 

 The removal of obstructions, and the construction of wing dams with 

 the material removed, will deepen the channel, by concentrating and 

 raising the current, and will have no perceptible effect upon the waters 

 of the upper river. 



Tli e Coal Me a sures. 



All that part of Rock Island county south and east of the Mississippi 

 and Rock river ranges of bluffs, is underlaid by the Coal Measures, 

 which, as we have seen, rest near the two rivers, and for several miles 

 back into the interior, upon the solid strata of the Hamilton limestone. 



