Page:History of Goodhue County, Minnesota.djvu/41

 H1STOKY OF GOODHUE COUNT* 15 having the power to abstrad Lime held in suspension in the water. ••Then came the interval between the Trenton and the glacial periods. The struggle between the ocean and the archsean con- tinent ceased. Minnesota and adjoining areas were raised above the sea. and our enmity began giving up instead of receiving more. Erosion sei in and the debris went elsewhere to build up other states, the archsean rocks in the meantime being completely worn down. The resull is in good part embodied in the topog- raphy we have today. The .Mississippi carved out its pivsenl channel but flowed aboul 100 feel Lower than it docs today. As the former periods were useful in building up the material for Red Wing's industries, so tins period was useful in exposing and making them easy of access. "Then came the glacial period. Geologists are very happy because of the fact thai an area of 10,000 square miles in Minne- sota. Wisconsin and Illinois was left uncovered by the ice fields. Of the driftless area. 3,000 square miles lie in Minnesota, and we are jusl about at the upper end of it. Maps of this period show thai glaciers bearing down on this region from the northeast seem to have spent their force and died away before they reached the lower driftless area. The glaciers from the Lake Superior and Michigan regions encircled it on the south, but did not cover it. hence, as Prof. Chamberlain said, the driftless area remains an unmarred monument of erosion from the earliest ages to the present time. The driftless area is clearly distinguished from the drifted area in that it is free from lakes, sloughs, or obstructed drainage. Gravid mounds, like those spread over the country from Hastings northward, are absent. No gravel is found beneath the soil except where running water lodged it. The valleys look old. The rivers that run from the glaciated to the drift- less area are lined by high terraces showing the height of the river bottom during the melting period of the glaciers, while the rivers lying wholly within the driftless area lack them. During the last glacial epoch, when the melting glaciers made a larger part of this county a great sea of icy water, gravel and sand were disengaged from the ice and carried forward to lower levels by turbulent waters. 'The valley of the Cannon river was flooded per- manently during the continuance of this whole epoch with waters that came directly from the ice fields of Dakota and Rice counties, and which bore along great quantities of floating ice and of mingled sand, mud and gravel. The Mississippi also was at flood stage. These valleys were filled with alluvial detritus to the height of their highest terrace, and flowed at a permanent level of about 125 to 150 feet higher than now, the bottom of the water being determined by this terrace. On the withdrawal