From the centre of the prairie the landscape rolled gracefully away towards the eastern timber, studded along its edge with farms. The retrospect from beneath the tall oaks of the prairie over which I had passed was exceedingly fine; the idea strikes the spectator at once, and with much force, that the whole plain was once a sheet of water. Indeed, were we to form our opinion from the _appearance_ of many of the prairies of Illinois, the idea would be irresistible, that this peculiar species of surface originated in a submersion of the whole state. There are many circumstances which lead us to the conclusion that these vast meadows once formed the bed of a body of water similar to the Northern lakes; and when the lowest point at the _Grand Tower_ on the Mississippi was torn away by some convulsion of nature, a uniform surface of fine rich mud was left. The ravines were ploughed in the soft soil by subsequent floods, and hence, while the elevated lands are fertile, those more depressed are far less so. The soil of the prairies is of a character decidedly alluvial, being composed of compact strata of loam piled upon each other, like that at the bottom of bodies of water long stagnant. The first stratum is a black, pliable mould, from two feet to five in depth; the second a red clay, amalgamated with sand, from {216} five to ten feet in thickness; the third a blue clay, mixed with pebbles, of beautiful appearance, unctuous to the feeling, and, when exposed to the atmosphere, of a fetid smell. Lakes are often found in the prairies abounding in fish, which, when the waters subside, are removed by cartloads. The origin of these vast prairie-plains is, after all, no easy matter to decide; but, whatever the cause, they have doubtless been perpetuated by the autumnal fires which, year after year, from an era which the earliest chronicles of history or tradition have failed to record, have swept their surface; for, as soon as the grass is destroyed by the plough, the winged seeds of the cotton-wood and sycamore take root, and a young growth of timber sprouts forth. The same is true along the margin of creeks and streams, or upon steril or wet prairies, where the vegetation does not become sufficiently heavy or combustible for conflagration to a great extent. These fires originated either in the friction of the sear and tinder-like underbrush, agitated by the high winds, or they were kindled by the Indians for the purpose of dislodging game. The mode of hunting by circular fires is said to have prevailed at the time when Captain Smith first visited the shores of Chesapeake Bay, where extensive prairies then existed. These plains, by cultivation, have long since disappeared. Mungo Park describes the annual fires upon the plains of Western Africa for a similar purpose and with the same result.[147] Tracts of considerable extent in {217} the older settlements of the country, which many years since were meadow, are clothed with forest.