108 GEOLOGY OF ILLINOIS. 



aqueous agencies. But in the parts of the county last mentioned, vast 

 accumulations of coarse gravel, commingled with fine white sand, have 

 been deposited, indicating that the drift forces and agencies acted here 

 on a large scale. Around the head-waters of Leaf river these gravel 

 hills are a marked feature in the landscape. About three miles and a 

 half north of Foreston, the Illinois Central Kailroad passes through a 

 range of these hills. The company have there opened many gravel 

 pits and quarries, and are constantly loading trains for the purpose of 

 ballasting their road. The appearance of that chain of hills is so re- 

 markable that few travelers on the swiftly-flying passenger trains fail 

 to notice and remark upon it. East of the track, a backbone of hills 

 stretch away toward Adeline, broadening and widening in the distance, 

 until they resemble great ocean waves fixed and solid. Our pocket- 

 level showed that the highest hump on this backbone, measuring from 

 the base, was about one hundred and three feet, while to the level of 

 the water in the brooks some distance off, the descent was probably 

 twenty feet. The railroad track ie cut through these gravel hills to the 

 depth of about forty feet. For that depth the material is composed of 

 gravel, from the size of pebbles to that of small boulders, mixed with 

 a large quantity of white sand. The sand is almost as white as the 

 St. Peter's sandstone, except where stained yellow by the oxide of iron. 

 The gravel is very much rounded and waterworu. The deposit has 

 marks of partial stratification in a few places. At one place, close to 

 railroad track, a bed of gravel, almost free from sand, is cemented so 

 strongly together by some calcareous substance, that it has to be quar- 

 ried like ordinary stone. It looks like a coarse conglomerate, or pudding 

 stone, and will resist, without breaking, a smart blow from a heavy ham- 

 mer. Such is the internal structure of these gravel hills. On the sur- 

 face they are covered with a thin soil, full of gravel and whitish boul- 

 ders of small size, into which a spade could not be sunk. Toward the 

 east the hills preserve their outlines for a distance of some eight miles 

 before they sink down into ordinary gravel beds, extending for a long 

 distance across the northern part of the county. Toward the west they 

 extend three or four miles before losing themselves in the general roll 

 of the prairies. The direction of the main chain is exactly east and 

 west; the western part, as indicated by a very good pocket compass, 

 bears west southwest by east northeast. 



A little brook runs toward the east on either side of the gravel hills, 

 being, perhaps, a quarter to half a mile apart. About the middle of the 

 range, the brook on the north side breaks through an abrupt gap, and 

 joins its sister on the south, and together they seek Leaf river, skirting 

 along the south side of the gravel beds. To the north and the south of 

 the small valleys, through which these little streams flow, the prairie 



