ROCK ISLAND COUNTY. 233 



tlu'i- extensions of old drifts, will doubtless afford profitable mining for 

 some years to come. The deposit however is quite local in extent, and 

 will some day become exhausted. In 1867 sixty-eight thousand tons of 

 coal were mined, and sent to market; in 1808 the amount was probably 

 larger. This, in time, will exhaust any small coal field. 



The coal itself is a fair, soft coal, tolerably free from sulphur, and 

 stained red in places with the rust of iron from the percolating waters. 

 Tt is well adapted to making; steam, for which purpose it is extensively 

 used. 



This seam nowhere perhaps rests directly upon the Devonian rocks, 

 as in Henry county, near Cleveland, but is separa ted therefrom by sand- 

 stones and shales, some twenty to sixty feet and upwards in thickness. 



The coal seams of Rock Island and adjoining counties along the 

 northern boundaries of the Illinois coal fields belong to the lower Coal 

 Measures of the State. The Silurian rocks dip very gradually, the 

 angle being almost imperceptible, beneath the Coal Measures. At 

 the south-west corner of Rock Island county the sub-Carboniferous lime- 

 stone probably underlies the Coal Measures ; at the mouth of Rock river 

 the Hamilton limestone does the same; farther up the river at Aldrich's 

 the Niagara limestone is the underlaying rock ; and along the northeast- 

 ern part of Bureau county the Galena limestone may be detected in the 

 same position. 



Ih-iff 7>;/o.s?7x. The usual Quaternary deposits are found in this part 

 of Hock Island county. In the south-west corner there is a strip of 

 alluvial bottom along the Mississippi river. On the south side of Rock 

 river tlw^ usual alluvial river bottoms extend across the whole county, 

 intersected with some low ridges of sand. Both these strips are inclined 

 to be swampy, except some portions of the latter, which are dry enough 

 to make excellent farming lands. The loess of the bluffs is not very 

 distinctly marked. A heavy deposit of light colored drift clays over- 

 lays the Coal Measures, attaining a thickness of fifty or sixty feet. Oc- 

 casional boulders are seen on the surface, or in the ravines. Gravel 

 beds and coarse gravel are not met with. No very marked drift phe- 

 nomena wen- noticed, and the drift deposits of the southern part of 

 Rock Island county present 110 peculiar or marked characteristics. 



Enmoinic'il Gfulof/t/. Of coal, the extent of its mining, and its proba- 

 ble supply, we have spoken already in a former part of this report. The 

 importance of the coal traffic in the future history of this county can 

 hardly be over-estimated. The facilities for distribution from Rock 

 Island into Northern Illinois and Iowa, and the great demand and easy 

 access to the Rock Island coal field for fuel to make steam on the Mis- 

 ppi river, create a steady demand for very large quantities of coal. 

 Tin- construction of a railroad up the valley of Rook river, and eventu- 

 al 



