TAZEWELL, Me LEAN, LOGAN AND MASON COUNTIES. 177 



In the greater part of Mason county, and over considerable tracts in the 

 southwestern part of Tazewell county, the surface configuration varies from that 

 which we have just described ; the prairies are low and comparatively flat, and 

 in many portions, were originally overflowed, or marshy, at some seasons of the 

 year. The soil of these prairies is a rich alluvium, generally more or less are- 

 naceous, which forms, when sufficiently elevated or drained, one of the best 

 producing soils in this district. Along the Illinois and Sangamon rivers in 

 this region, we find in some places rather extensive sandy tracts of river forma- 

 tion, and on the Sangamon river, in Mason county, and on the Illinois river, in 

 Mason and Tazewell counties, the bald bluffs of the Loess, are in some locali- 

 ties conspicuous features in the general landscape. 



The principal streams occurring in this district, besides the Illinois and 

 Sangamon rivers, which form a portion of its borders, are the Mackinaw river, 

 in Tazewell, Mason and McLean counties, Salt creek, in Mason and Logan 

 counties, and Kickapoo and Sugar creek in Logan and McLean counties. 

 These, with many minor streams, and nameless tributaries, drain nearly the 

 whole surface of this district. With the exception of the Illinois and Sanga- 

 mon rivers, none of the streams have very extensive adjoining tracts of bottom 

 land, and even along these rivers, the bottoms are frequently of inconsiderable 

 width, or wanting altogether. 



The principal kinds of timber found in the upland wooded tracts of this dis- 

 trict are nearly the same as those already enumerated as occurring in the 

 adjoining counties, namely, the principal varieties of oak and hickory, black 

 walnut, butternut, maple, bass-wood, red-bud, sassafras, etc. On the river bot- 

 toms, and in low damp lands generally, the sycamore, buckeye, black ash, elm, 

 etc., are abundant. The sandy ridges are generally covered with a growth of 

 scrubby oak and black-jack, with a thin admixture of other species. 



The geological formations appearing at the surface in this district, consist 

 almost entirely of the Drift and later formations, the older rocks outcropping 

 only at a comparatively few localities, in Tazewell and Logan counties. The 

 underlying rock, however, as far as can be ascertained from these outcrops, as 

 well as from artificial exposures by shafts, etc., in various parts of the district, 

 consists entirely of the different beds of the Coal Measure series. 



The Loess, the uppermost of the more recent geological formations, appears 

 only in the vicinity of the Illinois and Sangamon rivers, and consists here as 

 elsewhere, of buff or ash colored marly sand, containing fresh water shells of 

 existing species. It is not everywhere equally well developed, and in various 

 localities along the Illinois river, in Mason and Tazewell counties, it either does 

 not appear or is not at all conspicuous. It may be well seen, however, along 

 the Sangamon river, in Mason county, where it appears in the bald, rounded 

 bluffs, with occasional mural-appearing escarpments covering their summits, 

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