204 GEOLOGY OF ILLINOIS. 



annual deposits are building up the flood plain, and altogether the val- 

 ley of the river is becoming dryer, notwithstanding the constant rains 

 the past summer have swelled it to one of its most formidable floods. 

 Second, after leaving this low flood plain, a second bottom or river ter- 

 race may be noticed, elevated twenty or thirty feet above the flood plain. 

 This is the ancient flood plain of the river. It is composed of loamy clay, 

 with various quantities of sand intermixed, with occasional beds of river 

 gravel. It produces the very best crops, is easily worked, and in an 

 agricultural point of view is of the greatest value. Fresh water shell 

 deposits and remains are sometimes found in it, and in similar positions 

 in other parts of the north-w est shell heaps have been found, supposed 

 to be the remains of human feasts. It is a great deal older than the 

 present flood plain, but geologically is comparatively recent. The Crow 

 meadow r s, the Lacon prairies, and the second table on which is laid the 

 railroad from Bureau Junction to Sparland, and a few narrow strips 

 on the east side of the river, are about the extent of this river terrace, or 

 ancient flood plain of the Illinois river in this county. 



The two bluff ranges on either side of the Illinois river valley contain 

 deposits properly belonging to the loess formation. They are not pure 

 loess deposits however. Marly clays and sands intermingled with grav- 

 els are the nearest approach to the loess to be observed. These every- 

 where exist along the bluffs, and maybe noticed in excavations and 

 partial landslides. The eroding influences of the rains have cut them 

 into ravines and hollows, and carried much of the bulk into the valley 

 below. The loess mixture remains in considerable quantities however, 

 and is well adapted to fruit culture and the growth of the vine. The 

 foundations of the hills however, and most of their matter, is composed of 

 Coal Measure deposits, and the older drift clays. The upland prairi es 

 are covered with the usual drift clays, of a yellowish or bluish color, 

 similar in kind, in appearance and in depth to the drift clay deposits 

 covering most of the prairies of the northern part of the State. Away 

 from the river gravels few gravel deposits belonging to the older drift 

 period exist. Boulders are not so abundant as in more northern coun- 

 ties. Some large ones of porphyry, syenite, and flame-colored granite, 

 were observed on the terrace bottoms of the Illinois river. 



Coal Measure Deposits. Except the deposits of the Quaternary system 

 above referred to, the only outcropping formation in the county belongs 

 to the Coal Measures. Outcrops of this formation are not of frequent 

 occurrence. In all that part of the county east of the Illinois river Coal 

 Measure rocks scarcely outcrop at all. The prairies of eastern Marshall 

 county, comprising much the largest portion east of the river, are level. 

 Neither coal, coal shales or coal rocks outcrop or come near the surface. 

 At Rutland, near the eastern line of the county, a shaft has been sunk 



