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problems that has engaged the attention of all thoughtful people who have seen them before they were touched by the plow. Scientists have sought carefully for evidences to sustain the different theories advanced. Professors Whitney and Hall, who made early geological surveys and examinations of portions of Iowa, gave considerable attention to the origin of prairies. Whitney says:
“The cause of the absence of trees on the prairies, is the physical character of the soil, and especially its exceeding fineness, which is prejudicial to the growth of anything but a superficial vegetation. The smallness of the particles of soil being an insuperable barrier to the necessary access of air to the roots of deeply rooted vegetation. Wherever, in the midst of the extraordinary fine soil of the prairies, coarse and gravelly patches exist, there dense forests occur. The theory that fineness of soil is fatal to tree growth finds its most remarkable support in the fact that in southeast Russia the limits of the black soil of Russia is an earth of exceeding fineness, so fine indeed that it is with the greatest difficulty that the air can penetrate it so as to oxidize the organic matter which it contains. It is easy to see why plains are likelier than mountain slopes to be treeless, it being toward the plains that the finer particles of the material which is abraded from the higher regions is being constantly carried. The more distant the region from the mountains, and the broader its area, the more likely it is that a considerable portion of it will be covered with a fine detritus, whether this be of sub-aerial origin, or deposited at the bottom of the sea.
“The exceedingly fine soil of the typical prairie region consists in large part of the residual materials left after the removal by percolation of rain and other atmospheric agencies of the calcareous portion of the undisturbed stratified deposits, chiefly of the Paleozoic age, which underlies so large a portion of the Mississippi Valley. The finer portions of the formations of more recent age in the Gulf States have also over considerable area remained treeless.”
Professor James Hall says:
“Throughout the prairie regions the underlying rocks are soft sedimentary strata, especially shale’s and impure limestones. Most of these on exposure disintegrate readily and crumble to soil. The whole soil of the prairies appears to have been produced from such materials, not far removed from their present beds. The valley soil, containing a larger portion of coarse materials than that of the uplands, seems to have been adapted to the growth of forest vegetation. In consequence of this we find such
