Another climatic change slowly came, and the ice began to melt. Rivers were gradually formed, carrying on their turbid waters the soil made by the grinding ice. This was deposited over the surface of the State, forming yellow clay.
Professor Samuel Calvin, State Geologist for Iowa, has told how the soils of the State were produced by the action of the ice in the glacial period. He says:
“Glaciers and glacial action have contributed in a very large degree to the making of our magnificent state. What Iowa would have been had it never suffered from the effects of the ponderous ice sheets that successfully overflowed its surface, is illustrated, but not perfectly, in the driftless area. Here we have an area that was not invaded by glaciers. Allamakee, parts of Jackson, Dubuque, Clayton, Fayette, and Winneshiek counties belong to the driftless area. During the last two decades numerous wells have been bored through the loose surface deposits, and down into the underlying rocks. The record of these wells shows that the rocks surface is very uneven. Before the glacial drift which now mantles nearly the whole of Iowa was deposited, the surface had been carved into the intricate of hills and valleys.
“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 to the divides, six hundred feet 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 uniforms 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