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| 12 | HISTORY |
localities covered with an abundant growth of timber. We sometimes meet with ridges of coarse material, apparently drift deposit, on which from some cause there has never been an accumulation of fine sediment; in such localities we invariably find a growth of timber. This is the origin of the groves scattered over the prairies, for whose isolated position and peculiar circumstances of growth we are unable to account in any other way.”
Dr. Charles A. White, who made a later geological survey of Iowa, in discussing this subject says:
“It is estimated that seven-eighths of the surface of Iowa was prairie when the State was first settled. They are not confined to the level surface, but sometimes are quite hilly and broken; and it has been shown that they are not confined to any particular variety of soil, for they prevail equally upon alluvial, drift and lacustral. Indeed we sometimes find a single prairie whose surface includes all of these varieties, portions of which may be sandy, gravelly, clayey, or loamy. Neither are they confined to the regions of, nor does their character seem at all dependent upon the formation which underlies them; for within the State of Iowa they rest upon all formations from those of the Azoic to those of the Cretaceous age inclusive, which embraces almost all kinds of rocks. Southwestern Minnesota is almost one continuous prairie upon the drift which rests directly upon not only the hard Sioux quartzite, but also directly upon the granite.
“Thus whatever the origin of the prairies might have been, we have positive assurance that their present existence in Iowa and the immediate vicinity is not due to the influence of the climate, the character or composition of the soil, nor to the character of any of the underlying formations. The cause of the present existence of prairies in Iowa is the presence of autumnal fires. We have no evidence to show or to suggest that any of the prairies ever had a growth of trees upon them. There seems to be no good reason why we should regard the forests as any more natural or normal condition of the surface than the prairies are. Indeed it seems the more natural inference that the occupation of the surface by the forests has taken place by dispersion from original centers, and that they encroached upon the unoccupied surface until they were met and checked by the destructive power of fires. The prairies doubtless existed as such almost immediately after the close of the Glacial epoch.”
The International Cyclopedia, in an elaborate article on the prairies, says:
“The origin of the very fertile prairies of the valley of the Mississippi River proper has been the subject of many theories. How a soil so rich
