Page:History of Iowa From the Earliest Times to the Beginning of the Twentieth Century Volume 1.djvu/46

This page has been validated.

8

HISTORY

used these rich minerals in covering up the bald rocks and leveling the irregular surface of preglacial Iowa. The materials are in places hundreds of feet in depth. They are not oxidized or leached, but retain the carbonates and other soluble constituents that contribute so large to the growth of plants. The physical condition of the materials is ideal, rendering the soil porous, facilitating the distribution of moisture, and offering unmatched opportunities for the employment of improved machinery in all of the processes connected with cultivation. Even the driftless area received great benefit from the action of glacier, for although the area was not invaded by ice, it was yet to a large extent covered by a peculiar deposit called loess, which is generally connected with one of the later sheets of drift. The loess is a porous clay, rich in carbonate of lime. Throughout the driftless area it has covered up many spots that would otherwise have been bare rocks. It covered the stiff intractable clays that would otherwise have been the only soils of the region. It in itself constitutes a soil of great fertility. Every part of Iowa is debtor in some way to the great ice sheets of the glacial period.”

* * * *

“Soils are everywhere the product of rock disintegration, and so the quality of the soils in a given locality must necessarily be determined in large measure by the kind of rock from which they were derived.

“From this point of view therefore, the history of Iowa's superb soils begin with first steps in rock making. The very oldest rocks of the Mississippi Valley have contributed something to making our soils to what they are, and every later formation laid down the surfaces of Iowa, or regions north of it, has furnished its quota of materials to the same end. The history of Iowas soils, therefore, embraces the whole sweep of geologic times.

“The chief agents concerned in modifying the surface throughout most of Iowa since the disappearance of the latest glaciers have been organic, although the physical and chemical influences of air have not been without marked effect. The growth and decay of a long series of generations of plants have contributed certain organic constituents to the soil. Earth worms bring up the material from certain depths and place it in position to spread upon the surface. They drag leaves and any manageable plants into their burrows, and much of the material so much taken into the ground decays and enriches the ground to a depth of several inches. The pocket gopher has done much to furnish a surface area of loose, mellow, easily cultivated and highly productive soil. Like the earth worm, the gopher for century after century has been bringing up to the surface fine material, to the amount of several tons annually to the acre, avoiding necessarily the pebbles, cobbles and coarser constituents. The burrows collapse, the undermined bowlders and large fragments sink downwards, rains and winds spread out the gopher hills and worm castings,