406 ' rHE GEOLOGY OF MINNESOTA. 



[Terminal moraines. 



dred feet higher than its west side because the bed-rocks underlying the till 

 rise highest in that part of the county. 



For a correct understanding of the origin of the topographic features of the drift-sheet, we 

 need to review briefly the history of the glacial period. It is proved that this included several 

 epochs of severe cold in which nearly all of the state was buried beneath a thick sheet of ice like 

 that now spread upon the Antarctic continent and the interior of Greenland. Between these 

 cold epochs were others when a milder climate reigned, and these accumulations of ice were par- 

 tially or wholly melted away, giving place to animal and vegetable life upon the land, remains of 

 which are preserved in fossiliferous beds enclosed between deposits of till. At least two glacial 

 epochs have left very clear records of the extent reached by the ice-sheets. The earlier carried its 

 drift as far south as Saint Louis, and nearly to the Ohio river on the east, even crossing this river 

 at Cincinnati, as shown by Prof. Wright, and beyond the Missouri river on the west; but left a 

 driftless area, which was surrounded by this ice -sheet, in southwestern Wisconsin and portions of 

 the adjoining states, reaching from southeastern Minnesota eastward to the Wisconsin river and 

 southward to the northwestern corner of Illinois. The later ice-sheet, which moulded the surface 

 of this county, was of less extent. Its southern portion was divided into great lobes, somewhat as 

 the earlier continental glacier had been parted at the driftless area, though again confluent farther 

 south. The boundaries of this lobed ice-sheet of the last glacial epoch are marked by very distinct 

 series of terminal moraines, or belts of hilly and knolly drift, which appear to have been deposited 

 at the margin of the ice, corresponding to the drift heaped at the termination of alpine glaciers. 

 These moraines have been traced, in a very irregular, looped course, through Wisconsin, Minne- 

 sota, Iowa, and Dakota. The glacial lobe whose eastern portion covered Waseca county stretched 

 southeasterly from western Minnesota to central Iowa. Its eastern border, marked by moraine 

 deposits, reaches from the Leaf hills in southern Otter Tail county southeasterly by Glenwood in 

 Pope county to lake Minnetonka, and thence southerly, passing through Waseca, Steele and Free- 

 born counties, to the vicinity of Des Moines ; whence its western border, shown by the continua- 

 tion of this moraine, joined with the preceding by a U- sna P e d curve, extends northwesterly by 

 Spirit lake and through southwestern Minnesota, to the Head of the Coteau des Prairies, in Dako- 

 ta, twenty-five miles west of lake Traverse. The large area within this looped boundary was cov- 

 ered by ice so deeply that the pressure of its weight caused it to flow slowly outward from the 

 center, where its thickness was greatest, toward each side, accumulating these hillocks of drift at 

 its margin. At the same time a glacial current from the thicker northern ice was pushed south- 

 easterly along the axis of this vast lobe and was deflected into its outward currents, as the trunk of 

 a tree sends out divergent branches. 



The moraines formed at the borders of this ice-lobe, both on its east and west sides, are mainly 

 double, showing two well-marked bells of roughly knolly and rolling drift, each a few miles in width, 

 divided by a tract of smoother surface, from two or three to twenty-five miles wide. As the 

 course of this formation makes a loop like the letter U, having been accumulated by ice-fields 

 covering the district enclosed, the outer moraine on each side is known to have been first made ; 

 and then, after a retreat of the ice-sheet, probably followed by a re-advance, the inner moraine 

 was formed ; for the latter would have had its very uneven surface planed off and mostly leveled, 

 if it had been covered by a moving ice-sheet, forming terminal deposits beyond it. 



South from Faribault to the Iowa line the moraine accumulated on the 

 east side of this ice-lobe is twofold, and consists of approximately parallel 

 belts of knolly and hilly till, from one to several miles in width, extending 

 from north to south, between which intervenes a tract of gently undulat- 

 ing till, from six to fifteen miles wide. Of these the eastern or outer mo- 

 rainic belt extends through the eastern range of townships in Steele coun- 

 ty. The western or inner moraine lies in eastern Waseca county and the 

 southwest edge of Steele county, having a width that varies from three 







