Climate of Middle Illinois. 11 



TOPOGEAPHY. 



Geological Foemation and Soil. 



The country which the Illinois river is traversing is a plain, cut in by 

 valleys 30 — 60 meter deep, and very slightly sloping from the northeast 

 to southwest, as will show the elevations of the following points: The 

 Mississippi, at low water at Dubuque, is said to be 186 meter; at the 

 mouth of the Ohio, 83 meter; the water-shed between Lake Michigan and 

 the Des Plaines river about 190 meter. Between Rock river and the Mis- 

 sissippi there are single hills rising to an elevation of 375 meter above the 

 sea level, and 90 meter above the surrounding country. The River Des 

 Plaines, running in a distance of a few miles along Lake Michigan, unites 

 under 41°20^ north latitude with the Kankakee coming from Indiana, and 

 from there the river is called Illinois, running for sixty miles due west; 

 then for about one hundred and eighty miles in a southwesterly direction, 

 and empties into the Mississippi under 30°50^ north latitude, 122 meter 

 above sea-level. The descent is, in average, 14 decimeter per mile. About 

 one hundred and forty miles above the mouth is Peoria, situated on the 

 right bank upon two terraces, the first of which is 15 meter, the second, a 

 little over 60 meter above low-water mark. Between the two terraces 

 runs parallel with the river a depression, no doubt once a slough; the lower 

 terrace, being an old sand-bank, rises at the lower end in a sand-hill, which 

 was probably formed by a counter-current coming from the Kickapoo Valley, 

 and shutting up the slough. This process was probably going on about 

 the end of the drift period, but may be observed to-day on many rivers of 

 the West. The second terrace, of equal height with the bluffs on the east 

 side of the valley and about three miles distant, formed the oldest banks. 

 The bluffs do not run in a continuous, straight line, but are interrupted bv 

 shallow or often deep ravines. The river, widening fourteen miles above 

 Peoria, forms a sheet of water called Peoria lake, which at the lower end 

 is about 1,600 meter wide. From there the stream keeps an average width 

 of 270 meter. 



In spring the river does rise from low water (140 meter above sea- 

 level), 6 meter and then on the left bank the bottom-land is overflowed. 

 The lower end of the lake was, thirty years ago, much wider than now, a 

 little creek coming from the east, often changing channel, formed in the 

 meantime not less than eighty or one hundred acres of land, partly covered 

 already with cottonwood and willows, and increasing in a direction against 

 a narrow strip separating a slough from the river. Should, in the course 

 of time, the opening, left yet, be shut up, the slough will, drying up, turn 

 in a prairie: the same process that was going on in the past on the right 

 bank. Two miles farther downward the river bends and the bluffs border 

 the left bank, the bottom-landbeing on the right side, where the Kikapoo 

 creek enters from the west through a narrow valley with steep bluffs and 

 numerous coal mines. 



