514 SOILS. 



only here and there by sandy belts or ridges bearing inferior 

 growth, among which, again, the black-jack and post oaks, 

 with short-leaved pine, are conspicuous. But in a large portion 

 of Illinois, as well as in \Yestern Indiana, the oak forest is in- 

 terrupted by more or less continuous belts, and sometimes by a 

 wide expanse, of black prairie, generally treeless or bearing 

 only clumps of crab-apple and haw, and underlaid more or less 

 directly by the carboniferous limestones, whose disintegration 

 has materially contributed to the black prairie soils; which are 

 noted for their high and long-continued productiveness. The 

 lower ground is characterized, besides clumps of crab-apple 

 and red haw, by the frequent occurrence of the honey locust, 

 the lead plant ( Amorpha fruticosa), the button-bush (Ccphal- 

 anthus occidentalism, and among herbs by the polar plant 

 (Silphium laciuiatiitn), the prairie burdock (S. tcrcbinthin- 

 acciuti), the swamp rose-mallow (Hibiscus moscheutos) , the 

 sneezewort (Hclcninin autumnale) , the wild indigo (Baptisia 

 tinctoria and Iciicophcca). 



The black-jack and post oak are not nearly as frequently 

 found on the prairies of Illinois as on those of Mississippi and 

 Alabama ; but where they occur they assume a similar habit, in- 

 cluding the occurrence of the dwarfed, apple-tree-shaped form 

 on the low ridges with heavy yellow clay soil, that sometimes 

 intersect the prairies. The post oak. moreover, in a form quite 

 similar to that described as occurring on the Flatwoods of 

 Mississippi, forms the timber of the " post oak flats " occasion- 

 ally found between the low ridges bordering the streams, or 

 along the edges of the prairies. The herbaceous vegetation of 

 these post oak flats distinctly characterizes them as being poor 

 in lime. In the loamy uplands, where the calcareous ingre- 

 dient is more abundant, the open-headed form of the black- 

 jack and post oak are also found, interspersed with a luxu- 

 riant growth of black, red and white oak, with more or less of 

 hickory, which here assume a magnificent development, much 

 superior to that seen south of the Ohio. These yellow -loam 

 uplands correspond very closely in their soil-composition and 

 agricultural character to the brown-loam area of Mississippi 

 and Tennessee, which lies inland from the Loess belt. Where 

 these uplands approach the prairie or the outcrops of a lime- 

 stone formation, there is usually added to the oak growth the 



