It is manifest that if this process be continued, and if all the hills are like that described, the reduction of all these terraces and mounds is but a question of time, and we may look forward to the day when all this now wild and impassable country shall be but a prairie of gentle undulations and monotonous outlook, not dissimilar to the wide plains which even now stretch off far to the east to blend with the Missouri Valley. Every mountain shall be made low and every valley filled, and no force more violent be concerned than the gentle action of the wind and rain.
I have said that the detritus of the storm is non-precipitate, is borne away by the water; and yet some of the moving particles do find lodgment by the way. There is no such thing as a talus at the foot of the bluff, but after each flood a thin film of fine silt is spread over the plain, and the flat bottoms of the ravines are by imperceptible pace forever creeping up the wasting buttes, particularly of those remote from the river.
But such a butte as that described, while revealing much, does not reveal all the facts necessary to the full understanding of our subject. One of the first things to strike the attention of the tourist among the hills is the evidence of the wide-spread action of powerful heat. The bands of red which everywhere mark the landscape are certainly traces of some glowing fire. But what a fire! Here are whole beds of clay baked until they have taken on the color and character of hard-burned brick or unglazed pottery. The resonance of the dry fragments under the hammer or the wheels of our vehicle is precisely that of broken terra-cotta. Sometimes the top of the butte is bare and red; sometimes the whole mass, from top to bottom, has been burned, and at a distance seems like a brick-kiln fallen into ruin. The splintery fragments, broken as macadamizing stone, form over the entire surface a natural riprap, on which the elements spend their force in vain. Such buttes are not transient; the fire has saved them, and in this dry climate they may stand forever. Here and there, so hot has been the fire, that the clay has been not only baked but fused, and great clinkerlike masses rest upon the hill-top, thrust themselves out from the hillside, or stand naked like monuments on the plain.
In looking for the source of heat capable of producing such phenomena men seem instinctively to revert to volcanic fires, and the burned clay is everywhere designated scoria. In one place where the railroad cuts through a hill of this material we have "Scoria Cut," and scoria constitutes for miles the favorite ballast. But probably volcanic fires were never nearer than at present. Of crater, lava, trap, or other usual volcanic concomitants, there is not the remotest sign; but to-day, while we are theorizing over the matter, some of the furnaces which have baked all these regions are still glowing, the smoke yet ascends, and our own eyes may witness something of the transformation. The lignite-beds furnish the fuel, the slow-paced erosion lays the fuel bare,