CHAPTER VII. 



Sand plains— Mississippi hawk — Small-leaved elm — Wild 

 horses — Hail storm — Climate — Bisons — Grapes — Red- 

 sand formation — Gypsum. 



Extensive tracts of loose sand, so destitute of plants and 

 so fine a$ to be driven by the winds, occur in every part of 

 the saline sandstone formation southwest of the Arkansa. 

 They are, perhaps, invariably the detritus of the sand-rock, 

 deposited in vallies and depressions where the rapidity of the 

 currents of water has been checked by permanent obstacles. 

 1 his loose sand differs in colour from the sandstone, which 

 is almost invariably red. The difference may have been pro- 

 duced simply by the operation of water suspending and re- 

 moving the light colouring matter, no longer retained by the 

 aggregation of the sandstone. These fields of sand have 

 most frequently an undulated surface, occasioned, probably, 

 not less by the operation of winds than by the currents of 

 water. A few plum bushes, almost the only woody plants 

 found on them, wherever they take root form points, about 

 which the sand accumulates, and, in this manner, permanent 

 elevations are produced. The yucca angustifolia and the 

 shrubby cactus, the white argemone, and the night-flowering 

 Bartonia, are the most conspicuous plants in these sandy 

 wastes. 



Our course, on the 15th, led us twice across the bed of 

 the river, which we found one thousand and four hundred 

 paces in width, and without water, except in a few small 

 pools where it was stagnant. This wide and shallow bed is 

 included between low banks, sometimes sloped gradually 



