HENRY COUNTY. 187 



swamps; its few sand-lulls ; and its unequalled Green river, are the 

 most prominent characteristics of its surface topography, and do not 

 differ materially from those of adjoining counties north and east. 



Geological Formations . 



These consist of the usual Quaternary deposits, the lower Coal Meas- 

 ure x-rifs. and some low outcrops of the Hamilton and Niagara lime- 

 stones. The geology of the county at first thought appears quite simple; 

 but the paucity of stone quarries, and workable outcrops, over most of 

 the county, makes the problem more difficult than one would at first 

 imagine The best section I can construct will give the formations 

 about as follows; 



General Section of County. 



Alluvial deposits and Drift clays 50 to 100 feet. 



Lower Coal Measures 250 to 300 " 



Hamilton (Devonian) limestone '. 20 " 



"t Le Clair limestone 15 " 



In this section a very marked hiatus of Illinois rocks will be observed 

 between the Hamilton limestone and the Coal Measures. 



y;>ii/tira Limestone. In the bed of Rock river, where it first touches 

 the north-western boundaries of Henry county, and from thence about 

 half way to Cleveland, the soft, fine-grained, yellowish Le Clair lime- 

 stone shows itself, and is quarried during low stages of the river, at one 

 place to a considerable extent. The Coal Measures at Aldrich's, and 

 Johnson & Kent's coal mines, rest directly upon this member of the 

 Niagara limestone. Except this limited outcrop in the banks and bed of 

 Rock river, this formation cannot be said to be developed in the coun- 

 ty. At ordinary stages of water in that stream, the outcrop would hardly 

 be detected. With the exception of a few eucrinite stems, no fossils 

 wci.- noticed in it. 



Hamilton Group. On descending Rock river from the Niagara out- 

 crops, just mentioned, the lower division of the Hamilton limestone is 

 next discovered, commencing in the bed of the river about a mile and 

 a half above Cleveland, and continuing as the river flows to the west 

 line of the county, and thence west at intervals across Rock Island coun- 

 ty. A short distance above Cleveland, and two or three times below 

 it, in a distance of three miles, a short axis of upheaval appears to extend 

 from the river almost south across Rock river bottom, which is here 

 three fourths of a mile in width, and runs under the bluff' line. At these 

 places the Hamilton limestone comes to the surface of the ground, 

 where the rains or little streams have removed a few feet of the top soil. 

 These axes, or undulations, rise twenty-five or thirty feet above the low 



