BROWN COUNTY. 63 



The bottom lands adjacent to the Illinois river, possess a light sandy soil, 

 and when sufficiently elevated to be susceptible of drainage, and are protected 

 from the annual overflow of the river floods, they are very productive. The 

 timber of the bottom lands consists of cottonwood, soft maple, linden, ash, elm, 

 black and white walnut, pecan, hackberry, sycamore, swamp white oak, bur oak, 

 Spanish oak, coffee-nut, shell-bark hickory, honey locust, wild plum, crab 

 apple, dogwood, etc. Although much of this land is now too wet for cultiva. 

 tion, being subjected to overflow from the periodical floods in the river, yet its 

 surface is constantly rising, from the accumulations of sediment left by the 

 river floods, and by the material constantly being deposited upon it by the 

 wash from the neighboring highlands. Thus, the hills are being leveled, and 

 the valleys filled up, a process constantly carried on now, as in all past time, 

 by wMch, in the coming ages, every portion of the earth's surface will become 

 fitted for man's use, and be made subservient to his interests. Every year 

 adds to the area of tillable land on our river bottoms, and the time is not very 

 distant, when their entire surface will be susceptible of cultivation. 



Geology . 



The geological formationt of Brown county, comprise the Quaternary, the 

 lower portion of the Coal Measures, including the three lower coal seams, and 

 the two upper divisions of the Lower Carboniferous limestones, as they are de- 

 veloped in this portion of the State. The following section will show the rela- 

 tive position and thickness of the formations above named, as they appear in 

 this county : 



FEET. 



Quaternary System, including Alluvium, Loess and Drift 80 to 110 



Coal Measures , 130 149 



St. Louis Limestone 30 " 40 



Keokuk group 40 60 



The Quaternary System includes all the superficial beds of soil, sand, clay, 

 gravel, etc., which cover up all the older formations, except along the streams 

 where the Lower Carboniferous limestone has been laid bare by the action of 

 running water. It is the newest, or last formed of all the geological systems, 

 and includes among its fossils, only the living species of animals, and those 

 closely allied to them. The term Alluvium, includes the surface soil and sub- 

 soil of the prairies, and the bottom lands along the borders of our rivers and 

 smaller streams. Possibly, the former may correspond nearer, in the time of 

 its formation, with the Loess, than with the deposits of the river valleys, but 

 it has generally been considered as coincident with the latter, in its formation, 

 and hence of Alluvial age. The Alluvium of the Illinois river valley, like 

 that of the Mississippi, consists, so far as we may judge from the exposures in 



