8 | HISTORY |
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“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,