‘Some have imagined that our prairies have been lakes; but this hypothesis is not tenable. If the whole state of Illinois is imagined to have been one lake, it ought to be shown that it has a general concavity of surface. But so far from this being true, the contrary is the fact; the highest parts of the state are in its centre. If we suppose, as some assert, that each prairie was once a lake, we are met by the same objection; as a general rule, the prairies are highest in the middle, and have a gradual declivity towards the sides; and when we reach the timber, instead of finding banks corresponding with the shores of a lake, we almost invariably find valleys, ravines, and water-courses depressed considerably below the general level of the plain. ‘Wherever hills are found rising above the common plane of the country, they are clothed with timber; and the same fact is true of all broken lands. This fact affords additional evidence in support of our theory. Most of the land in such situations is poor; the grass would be short, and if burned at all, would occasion but little heat. In other spots, the progress of the fire would be checked by rocks and ravines; and in no case would there be that accumulation of dry material which is found on the fertile plain, nor that broad, unbroken surface, and free exposure, which are necessary to afford full scope to the devouring element. ‘By those who have never seen this region, a very tolerable idea may be formed of the manner in which the prairie and forest alternate, by drawing a colored line of irregular thickness, along the edges of all the water-courses laid down on the map. This border would generally vary from one to five or six miles, and often extend to twelve. As the streams approach each other, these borders would approach or come in contact; and all the intermediate spaces not thus colored would be prairie. It would be seen that in the point formed by the junction of the Ohio and Mississippi, the forest would cover all the ground; and that, as these rivers diverge, and their tributaries spread out, the prairies would predominate.’