170 GEOLOGY OF ILLINOIS. 



QUATERNARY DEPOSITS Alluvium. The Illinois river bottom, on 

 the west side of the river, lies in the county of Bureau from three miles 

 below Peru to the south line of the county, a distance of from fifteen to 

 eighteen miles in length. At its upper end it is not much over a quar- 

 ter of a mile wide ; at its lower, it gradually spreads out to a mile or 

 mile and quarter. For most of this distance there are two bottoms. 

 The first and widest is a low flat expanse, composed of sloughs, river 

 sand beds, finely comminuted black mud banks, boggy and mucky mea- 

 dows, covered with a dense growth of wild grasses, and green scum- 

 covered ponds, starred with water lilies. Most of this first bottom is 

 subject to the annual overflows of the Illinois river. Very little of it is 

 susceptible of cultivation, but where dry and high enough to be culti- 

 vated, it yields immense crops of Indian corn. The slough or lake 

 on which the village of Trenton stands, runs up along the west side 

 of this bottom for several miles. For part of this distance a heavy belt 

 of bottom timber skirts the Illinois river. Some of the bogs, morasses, 

 and sloughs in this low bottom, covered with green scum and almost 

 seething beneath a summer sun, have a Stygian smell, and must be pro- 

 lific breeding places for agues and intermittent fevers. The name Leper- 

 town, applied to the part township lying along the Illinois river, is no 

 misnomer. 



I do not know the depth of this black, alluvial deposit of river mud 

 and sand, but it is quite deep, perhaps thirty or forty feet in many 

 places. 



From forty to fifty feet above this first bottom of the Illinois river, 

 and lying along its western bluif range, is another or second river bot- 

 tom or terrace. This one is from a few hundred yards to half a mile or 

 more in width. It seems to be composed of sandy and marly clays, in- 

 termixed in places with marly-mixed gravels. It is a regular river ter- 

 race. Its eastern line is the old shore of the Illinois river. The rail- 

 road track is built along this river shelf or terrace, and the traveler, 

 from the car window, obtains a fine view of the valley of the river, 

 stretching away with its dark serpentine belt of timber, and glimpses 

 of the slow-moving, shining water. In the diluvial epoch, when the 

 water spread all over the low bottom, the Illinois river, lake-like in its 

 expanse and slowness of current, must have presented a body of water 

 larger than the Mississippi in its ordinary or even high stages of water. 



The lower valley of Big Bureau creek has also a narrow alluvial bot- 

 tom, back a few miles from its confluence with the Illinois river. This 

 bottom is narrow, crooked, and covered with timber. The deposit is a 

 rich, fat, marly one. A few small farms are opened in it below Tis- 

 kilwa. These farms are immensely productive. 



