502 
200 feet. There are no natural outcrops of the underlyine noes 
within the county limits. é 
A glance at a map representing the rivers of the state will show 
that a number of important rivers rise either within the county or 
immediately north of it and flow in all directions but a northerly 
one. The Sangamon crosses the northwest corner of the county, and 
with several prairie streams or tributaries drains that quarter of the 
county. The Middle Fork of the Big Vermilion (of the Wabash) 
just enters the northeast corner, and the various branches of the 
Salt Fork of the same river drain the most of the eastern half of the 
county. The southwest quarter is drained by the head waters of 
the Kaskaskia and Embarras rivers. These last two streams are in 
this section little more than prairie creeks with steep earth banks 
and undeveloped treeless valleys. The Sangamon and the larger 
tributaries of the Big Vermilion have the same general character- 
istics. In the vicinity of the moraines they lie in narrow, well-defined 
valleys, which usually rise in steep bluffs on one side, 30 to 70 feet 
or more in height. The flood-plain, usually narrow, may reach a 
quarter of a mile in width. Beyond the moraines, in the till, the 
valleys are lower and not so well defined. All these streams are 
subject to heavy floods. In summer, however, their muddy waters 
flow between steep earth banks 4 to 8 feet below the flood-plain. 
Originally a belt of timber, sometimes narrow, but sometimes 
attaining a width of nearly two miles, extended along these larger 
streams. It was almost invariably broader on the east and north 
sides of a stream than on the west and south sides, a possible ex- 
planation being that woods on the south and west would be more 
exposed to prairie fires driven by the prevailing southwest winds. 
It is needless to say that this primitive condition has been greatly 
modified since the settlement of the country. The steep bluffs 
along the rivers are in general still covered with timber, though it is 
usually of small size and recent growth, and dense thickets and woods 
with heavy undergrowth still occur along the river valleys and on 
the flood-plains; but, for the most part, the broad belt of forest that 
formerly encroached on the prairies along the streams is represented 
only by scattered groves of second growth, and these are usually 
much thinned out, and the underbrush is kept down by grazing. 
These river-belt areas still furnish the chief cover and highway for 
the migration of many of the larger mammals left within our area. 
