Page:History of Goodhue County, Minnesota.djvu/39

 HISTORY OF GOODHUE COUNTY 13 ness. Their size is fairly uniform iu the same layer. The lower layers contain coarser grains and the succeeding higher ones liner grains. "At Claybank can be seen the clay pits. At Wanamingo the limestone quarries are filled with mummies of countless crea- tures, while on the fields are boulders of volcanic rock, covered everywhere in our county, as with a mantle, by till and loam. Along our rivers lie the terraces and gravel bars which add so much to the beauty of our deeply-eroded valleys. The above features constitute the main geologic formations of Goodhue county. The story of these formations is believed by geologists to be about as follows : The hard archaen rocks revealed by borings represent the ancient sea bottom when the earth had cooled sufficiently to form an outer crust and the vapor of the atmosphere had become sufficiently chilled to form the sea, which covered the outer crust. Then the nucleus of America appeared at the north. The sea had a powerful sweep against the newborn land. The absence of vegetation favored swift drainage. The high rate of the earth's revolution favored the formation of rapid ocean currents. The tides produced by such a rapid motion hurled themselves with fury in quick succession upon the beach. The higher temperature of the atmosphere favored, torrential rains and produced most violent storms. The presence of many gases and acids and the barren ness of the land all favored the rapid disintegration of the rocks under the attacks of the atmos- phere, while the heaving of the sea washed the debris back, scattering it over the floor of the sea. The finest parts were carried furthest, so that the sand in our county is a testimony of the comparative shallowness of the former sea. The grains of sand were sifted, sorted and smoothed in their journey. This explains also the fact that the grains in any one layer are fairly uniform in size. The difference in color is due to storms or later infiltrations; coarser or finer grains determine greater or less distance transferred. The succession of sandstone, shales and limestones is due to the successive rising and sinking of the ocean surface. The shales were formed by the stirring up and blending of the sand with the new material coming in above it. The limestones were deposited in quiet, deep waters, but the succeeding elevation permitted the waves to stir them up in places into dome-shaped structures and knolls of varying thick- ness. "Wherever the sea encroached on the northern land, the sand was left further north, and we received the finer materials. When the sea receded it washed backward the sand upon the deeper formation. That our rocks are sea deposits is shown by several clearly read proofs. 1 — The nature of the material and character of the grains of sand and lime. 2 — Their horizontal