»roEE.] KANSAS CITY TO CHICAGO. 451 



of the middle Carboniferous sea j but within 25 miles east of Mississippi 

 river the rocks come to resemble more closely those characteristic of 

 the Coal Measures of the Illinois-Indiana basin. The sandstones near 

 the river, and the shales and limestones (with a few coal scams) of the 

 interior, rest unconformably on the older strata; for the calcareous series 

 of deposits, commonly referred to the sub-Carboniferous, is absent, 

 and the Devonian, broadly developed in Iowa, soon fails, leaving the 

 Carboniferous and Silurian strata nearly or quite contiguous. 



On approaching Davenport the railroad passes through deep cuts 

 in Pleistocene deposits, which afford interesting sections. The upper- 

 most deposit is loess, somewhat more clayey than that of Missouri 

 river, yet abounding in similar fossils; its thickness ranging from 10 

 to 30 feet. At its base it commonly becomes gravelly or grades into an 

 attenuated drift sheet; and loess and drift alike rest on an ancient 

 soil, or "forest bed," which has yielded not only abundant remains 

 of coniferous woods, but also bones and tusks of the elephant. Below 

 lies a dense, tenacious drift sheet, representing the earliest well-defined 

 ice invasion of the Pleistocene. 



Between Davenport and Rock Island the Mississippi flows in what 

 may be styled, for that stream, a contracted gorge, half a mile to a mile 

 in width. This gorge opens immediately below the cities; upstream 

 it extends for some 25 miles to the town of Le Claire. Throughout 

 this stretch of relatively narrow channel the current is exception- 

 ally strong, particularly at the upper and lower extremities. Thus 

 the terms " Pock Islands Papids" and "Le Claire Rapids" have long 

 been familiar to the pilots and captains of the packets plying between 

 St. Louis and St. Paul, and, indeed, to other rivcrmen. Formerly 

 the rocky islet, from which the Illinois city takes its name, was sepa- 

 rated from the mainland of Illinois by a navigable channel, and indeed 

 represented nothing more than the largest of a series of "reefs" rising 

 from the river bottom. Subsequently the Iowa channel was deepened 

 and the Illinois channel was finally dammed to afford waterpower for 

 the United States Arsenal located upoi the island. 



The only rocks exposed in the immediate vicinity of Davenport and 

 Rock Island are Devonian; they are fossiliferons, and, for the most 

 part, have been correlated with the Hamilton of New York; but their 

 exact position in the geological scale can not be said to be finally deter- 

 mined. Exposures of brown Carboniferous sandstone occur within a 

 tew miles of both cities. 



A few miles east of Rock Island the railroad approaches and finally 

 <-rosses Pock River, which, it may be observed, fiows in a dispropor- 

 tionately broad gorge. Moreover, it may be noted that this valley 

 bifurcates, sending its principal arm northward to be occupied only by a 

 t rifling stream, while the narrower is marked by the course of Pock river. 



