"To a person passing from the drift-covered to the driftless part of the state, the topography presents a series of surprises. The principal drainage streams flow in valleys that measure, from the summits of the divides, six hundred or more in depth. The Oneota, or Upper Iowa River, in Allamakee county, for example, flows between picturesque cliffs that rise almost vertically from three to four hundred feet, while from the summit of the cliffs the land rises gradually to the crest of the divide, three, four or five miles back from the stream. Tributary streams cut the lateral slopes and canyon walls at intervals. These again have tributaries of the second order. In such a region a quarter section of level land would be a curiosity. This is a fair sample of what Iowa would have been had it not been planed down by the leveling effects of the glaciers. Soils of uniform excellence would have been impossible in a non-glacial Iowa. The soils of Iowa have a value equal to all of the silver and gold mines of the world combined. "And for this rich heritage of soils we are indebted to great rivers of ice that overflowed Iowa from the north and northwest. The glaciers in their long journey ground up the rocks over which they moved and mingled the fresh rock flour from granites of British America and northern Minnesota with pulverized limestones and shales of more southern regions, and used these rich materials 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 largely 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 glaciers, 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. * * * * *