212 GEOLOGY OF ILLINOIS. 



and is, at the longest measurement, about fifteen miles long from north 

 to south, and about twenty-five miles from east to west. 



Surface Configuration. The most marked feature in the surface con- 

 figuration of the county is the Illinois river and its attendant bluffs and 

 bottoms. The river itself flows along the northern boundary line of 

 the county from, the north-east to the north-west corner of the county, 

 at which latter locality it makes its great bend from a western to a 

 southern course. It flows along the western boundary line until it 

 reaches the township of Snatchwine, which township it leaves 011 the 

 west. The river bottom, within the boundaries of this county, is not so 

 extensive as in other counties in this part ot the State. On the eastern 

 side the bluff range keeps near the river through the entire extent of 

 the county. About Hennepin, and immediately below, it is a sort of 

 high prairie, rising gradually back from the river. This is a sort of 

 medium table land between the alluvial bottom and the highlands back 

 from the bluff range. It is very fertile, but rather sandy, and is under 

 a high state of cultivation. On the west side of the river, from its en- 

 trance into the county to the south line of the same, the river bottom 

 is from one-half to about two miles in width, except at the southern 

 boundary line, where it widens out into the upper extremity of the 

 " Crow Meadows," in Marshall county. This stretch of alluvial bottom 

 laud is subject to almost annual inundations from the overflow of the 

 Illinois river. It is one interminable wilderness swamp, penetrated 

 with sloughs and swales, overgrown in places with thickets of water- 

 willow, dense with heavy grasses thickly interwoven with pea vines, 

 receiving from each overflow a deposit of soft mud silt, with one or two 

 slough-like expanses or lakes during low water ; a broad expanse of 

 yellow, thick, cream-colored w T ater at high flood of the river ; a pesti- 

 lent tract, breeding fevers, frogs and niosquitos ; skirted in two or three 

 places with bottoms high and dry enough for cultivation. Such is the 

 character of this bottom. In it there is some heavy timber skirting 

 the river. Banks of sand and fields of mud and silt alternate along 

 the stream. 



The bluff ranges on both sides of the river have nothing peculiar 

 about them. They rise to an altitude of from 80 to about 125 feet, For 

 the most part they are gently rounded and covered with a light growth 

 of scattering timber. They are composed for the most part of drift 

 clays, and gravels, "and Coal Measure deposits, occasionally showing 

 loess, marly clays, and sands. From the brow of these bluffs, in either 

 direction from the river, is a tract of rough or barren land from one to 

 about four miles in width. These strips of land are somewhat rough ; 

 are intersected by numerous ravines, and are more or less covered with 

 a scattered growth of oak timber. These rough lands, although not so 



