OF ARKANSAS. 325 



prairie. In this case, as coarser materials are of course heaped on the 

 banks of these creeks, a few trees grow along them. They are mostly 

 stunted specimens of the Post-Oak, the Eock Chestnut Oak, the Persimmon, 

 the Mockernut, the Juniper, and a shrub, Bumelia lanuginosa, Pers. The 

 characteristic herbaceous plants of these limestone prairies are especially: 

 Ambrosia polystacliya, Kuhnia Eupatorioides, Aster sericeus, Croton capita- 

 turn, Grindelia lanceolata, Palafoxia callosa, Oxibaphus albidus, &c, species 

 which are not found on the prairies of other formation. Besides these 

 plants they are covered with a great number of species belonging to the 

 prairies in general. 



Between this and the second division of the prairies, viz., of those which 

 are formed on the Carboniferous shales and clay, there is a remarkable 

 transition, which unites both divisions, or rather shows their common 

 origin. In the western parts of Benton and the northern part of Washing- 

 ton counties some flat prairies, formed like those of the second division, 

 and underlaid by shales or red clay, have still at their surface some isolated 

 patches of Subcarboniferous cherty limestone, which appear here and there, 

 breaking the general horizontality like small mounds. Possibly these low 

 mounds could support the vegetation of the trees, and they may have been 

 transformed into prairies by the influence of fire, which is a secondary 

 agent of their formation. But the soil which covers them is exactly of the 

 same nature as the soil of the surrounding prairies, and as their height is 

 no more than two or three feet, they may have been formed in the same 

 manner and by the agency of water. 



' 2d. The prairies on the Carboniferous shales are generally flat, sur- 

 rounded by hills, or at least by a higher border, which gives them the 

 appearance of the bottom of drained lakes. These prairies are of various 

 extent, and although they may overlie different kinds of ground or geo- 

 logical formation, in Arkansas they are generally underlaid by Carbon- 

 iferous fire-clay or shales. In the spring they are covered with water 

 which cannot percolate, and become true marshes for a time, and have 

 the vegetation of marshes : the rushes and the sedges. This semi-aquatic 

 vegetation gives, according to the nature of the underlying strata, either 

 a hard, compact, cold soil, by decomposition of shales or clay ; or, when 

 mixed with sand, the peaty black soil of the prairies of Illinois and of the 

 Northern States. In the summer months, these marshy prairies become 

 dry by evaporation, and as it happens with the prairies of the first section, 

 the alternative of too much water and of dryness in the soil prevents the 

 growth of trees. 



These prairies are more sterile or rather more difficult to cultivate than 

 those of the former section, as we shall have occasion to see when exa- 

 mining the counties of Sebastian, Franklin, &c, where this kind of prairie 

 is mostly found. A few trees, — the Water Oak, the Pin Oak, the Honey 



