Abstract

County photo-indexes of glaciated areas of South Dakota and Minnesota show scattered areas of definite pattern similar to those of the Mankato lobe in Iowa.

The areas of best-developed pattern are in southeastern South Dakota, adjacent to James River, and in southern Minnesota, in Brown, Cottonwood, Martin, and Watonwan counties. The pattern is interpreted as resulting from the presence of deposits made annually in the course of glacial retreat. Most of these have low relief and constitute minor moraines. The front of the ice as outlined by them is not in accord with the general front of retreat as deduced from the major recessional moraines mapped by earlier geologists. Minor moraines, where present in areas mapped as recessional moraines by others, do not generally parallel them in strike. The greater part of the areas of minor moraines lies outside these areas of recessional moraines as mapped by others. The areas are generally of relief less than 30 feet per square mile.

A second type of pattern, present in Morrison County, Minnesota, results from the presence of low swells up to half a mile in width, separated by intervening swales, of equal width, with relief of approximately 50 feet. The photo-index of Hubbard County, Minnesota, discloses an area of pattern of crowded ridges having a relief of 200 feet. Still other areas of other parts of the two states have areas of patterns of variable distinctness, size, and character. Materials are largely till.

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