These vast plains of Louisiana, near the upper courses of the Arkansaw, with its tributary streams, and the head-waters of the Kanzas, White and Grand Osage rivers, may become in time like the sandy deserts of Africa; ‘for,’ says Pike, ‘I saw in my route, in various places, tracts of many leagues, where the wind had thrown up the sand in all the fancied forms of the ocean’s rolling waves, and on which not a single speck of vegetation appeared.’ From this circumstance Pike deduces the following remark: ‘From these immense prairies may arise a great advantage to the United States, namely, the restriction of our population to some certain limits, and thereby a continuation of the Union. Our citizens being so prone to rambling, and extending themselves on the frontiers, will, through necessity, be compelled to limit their extent on the west to the borders of the Missouri and Mississippi; while they leave the prairies, incapable of cultivation, to the wandering and uncivilized aborigines of the country.’ These prairies, from the borders of the Mississippi, on the east, to the base of the Mexican Alps on the west, rise with a continually increasing acclivity for many hundred miles, till, at the base of the mountains, they attain an elevation of eight thousand feet, as we are informed by Pike, which is greater than the elevated level of the great desert of Gobi, on the north-west of China, estimated by Du Halde to be five thousand five hundred and eleven feet above the level of the sea, or the great arid desert, to the north of the cape of Good Hope, traversed by the Orange river, and lately visited by the Rev. Mr. Campbell, the elevation of which is estimated by Colonel Gordon at six thousand five hundred and sixty-one feet above the level of the sea. In addition to the aridity of the Louisiana prairies, they are so impregnated with nitre, and other salts, as to taint the waters that flow in various directions. Pike says, that for leagues together, they are covered with saline incrustations; and a number of tributary streams descending into the Arkansaw and Kanzas rivers are perfect salines; and beyond the river Platte, as we are informed by Colonel Lewis, the lands are not only destitute of timber, but even of good water, of which there is but a small quantity in the creeks, and even that is brackish. The same saline incrustations pervade the prairies on the Upper Missouri; and the same want of timber, little or no dew, with very little rain, continues till the neighborhood of the mountains.