2 28 THE POPULAR SCIENCE MONTHLY. 



closing bluffs here vary from seventy-five to a hundred feet in 

 height, being frequently cut back by ravines, as already described. 

 The level of the Illinois River at this point is a little under four 

 hundred and fifty feet. The floor of the old channel stands at 

 four hundred and seventy feet. Its descent from Summit Station 

 is therefore one hundred and twenty feet in about seventy miles ; 

 but it must be remembered that part of this slope may be due to 

 post-glacial elevation of the land to the northward. 



The entrance of the Fox River from the north at Ottawa was 

 one of the special features that I wished to see. It runs near the 

 western base of the Marseilles morainic belt, and its trench below 

 the general upland is as deep as the old channel ; but it is narrow 

 and steep-sided, like the many side ravines of the old-channel 

 bluffs, although in volume the Fox is at least half as great as the 

 Illinois. It has a flood plain of slight width where its banks are 

 of fire clay, as at Dayton, three miles from Ottawa ; but farther 

 up and down stream, where it is inclosed by sandstones, the rocks 

 rise directly from the water's edge, and steep bluffs rise above the 

 rocks to the upland. The descent of the river bed is relatively 

 rapid, amounting to about sixty feet in the first ten miles above 

 its mouth. 



The other rivers that enter the old channel present the same 

 peculiarity as the Fox, but as they come in over lower ground 

 their valleys are less deep, and therefore less noticeable. The 

 Desplaines has already been described as flowing in a narrow 

 trench in the plain west of Chicago, until it abruptly enters the 

 swampy bed of the old channel. The Kankakee has a similar 

 narrow valley when it joins the Desplaines, from the southeast, 

 in the Morris basin, the two rivers forming the Illinois. Next is 

 the Fox, and below this is the Vermilion, with a steep-sided, 

 narrow valley like those of its fellows. The contrast between the 

 narrow valleys of the side streams and the broad channel followed 

 by the Illinois is strongly marked. 



This is all plain enough on the ground ; it is distinctly shown 

 on the maps ; but it should also be represented by photographs. 

 If any readers of this article happen to have views illustrative of 

 the district here described, I beg that they will communicate with 

 me. There should, indeed, be a photographic exchange estab- 

 lished by a union of our professional and amateur photographers, 

 in which good views might be selected under certain conditions 

 for purchase or exchange. At present it is a very difficult matter 

 to find views of the simpler landscapes of our country, however 

 well represented the greater mountains may be. 



AVhen all these features are considered together, there is good 

 warrant in the old belief of the southwestward overflow of Lake 

 Michigan. The considerable breadth of the old channel, in which 



