494 THE GEOLOGY OF MINNESOTA. 



[Topography. 



crossed by the west line of this township; Flaherty's lake, a mile or more in length from north to 

 south, and a half mile wide, in sections 6 and 7, Heron Lake; Boot lake, a mile long from north 

 to south in sections 30 and 31, Belmont; Clear lake, exceeding a mile in length from east to west 

 and about three- fourths of a mile wide, at the west side of Des Moines; Loon lake, nearly two 

 miles long from north to south, crossed by the east line of Minneota; the Little Clear lakes, in 

 sections 22 and 23 of this township; Little Spirit lake, about a mile in diameter, lying mainly in 

 section 35, Minneota, divided from Spirit lake in Iowa by only a narrow low ridge of gravel and 

 sand, pushed up by ice during the recent period; Skunk lake, a mile long from east to west, lying 

 mostly in the south half of section 22, Sioux Valley; Rush lake, also a mile long, but trending 

 from north to south, in the southwest part of the same township; Hum Island lakes, a half mile 

 and one mile long, near the middle of Round Lake township; Round lake, a little more than a mile 

 n diameter, in the northwest part of this township; and State Line lake, a mile long from north 

 to south, situated at the southwest corner of the county. 



Topography. In northern Cottonwood county a massive ridge of the red 

 Potsdam quartzyte extends twenty-five miles from west to east through 

 Storden, Amboy, Delton and Selma, terminating in the west edge of Adrian, 

 the northwest township of Watonwan county. This highland is mostly 

 covered by a smooth surface of till, but has frequent exposures of the rock. 

 Its altitude increases from 100 feet at its east end to 300 feet westward, 

 above the broad, slightly undulating sheet of till, which, excepting a mo- 

 rainic tract in Stately, covers the region toward the north. The hight reached 

 at the top of this quartzyte ridge, 1306 to 1500 feet above the sea, is a per- 

 manent rise of the land, which to the south and southwest holds nearly 

 this average elevation, with a general ascent westward. 



This ridge was probably considered by the early French explorers as the northeast border 

 of the Coteau des Prairies, which name, meaning the Highland of the Prairies, they gave to an 

 elevated tract, extending about two hundred miles from north-northwest to south-southeast in 

 eastern Dakota and southwestern Minnesota. Of this highland in Cottonwood and Murray coun- 

 ties, Nicollet says:* "Under the forty-fourth degree of latitude, the breadth of the Coteau is 

 about forty miles, and its mean Elevation is here reduced to 1 ,450 feet above the sea. Within 

 this space its two slopes are rather abrupt, crowned with verdure and scolloped by deep ravines 

 thickly shaded with bushes, forming the beds of rivulets that water the subjacent plains." It is 

 not continuously recognizable as a great topographic feature south of this quartzyte ridge. 



The Little Cottonwood river and the north branch of the North fork of Watonwan river 

 flow northeasterly through gaps in the range of quartzyte, a hundred feet or more below its crest, 

 the former finding its passage at the middle of the north half of Delton, and the latter about a 

 mile west from the center of Selma. Excepting at these points, the ridge is unbroken and up- 

 lifts a broad, smoothly rounded top, covered with till through which the quartzyte has occasional 

 outcrops. It extends in a course a little to the north of west twelve miles from the north part of 

 section 25. Selma, to the north part of sections 9, 8 and 7, Delton; and thence a little to the south 

 of west ten miles to Highwater creek at the middle of Storden township. In its east half, through 

 Selma and Delton, this ridge has a width that increases toward the west from a half mile to one 

 or two miles, elevated 50 to 100 feet above the average of the land for the next live or six miles 

 to the south, and twice this hight above the country which it overlooks northward to the horizon. 

 Both slopes of the range have a gentle descent, that to the north occupying a width of one to two 

 miles, and reaching from section 7, Delton, to the falls formed by this quartzyte on the head- 

 streams of Mound creek, in the southwest corner of Brown county, and in the N. E. } of section 



'Report on the upper Mitsissippi rivef, 1843, p. 10; consult also plate 7 and page 68 uf the present volume. 



