572 THE GEOLOGY OF MINNESOTA. 



[Potsdam quartzyte. 







strata are exposed in a ravine north of the Minnesota river, opposite to Minnesota Falls; in the 

 gorge of the Kedwood river, below Redwood Falls; in many of the ledges of the Minnesota valley 

 for several miles next below, especially in excavations made by roads at the foot of the bluffs; in 

 the valley of Birch Cooley near its mouth; and occasionally for eight or ten miles farther south- 

 east. They have been found also in well-digging at considerable distance from the Minnesota 

 valley. 



Potsdam quartzyte. The red quartzyte of southwestern Minnesota is 

 destitute of fossils, but from its stratigraphic relations it appears to belong 

 to the Potsdam age. Its outcrop two to three miles southeast from New 

 Ulm lies in Nicollet county, to the report of which the reader is referred 

 for its particular description. The only outcrop of this formation within 

 the district here reported is in Brown county, less than a mile from its 

 southwest corner, being in section 31, Stately. 



This is the north edge of a large area upon which this rock forms a massive ridge, in north- 

 ern Cotton wood county, 200 to 300 feet high, and reaching about twenty-five miles from east to 

 west, mostly overspread by smooth glacial drift. In the north part of section 31, Stately, this 

 red quartzyte, or metamorphic sandstone, occurs in its typical character, being very hard, vary- 

 ing in color from reddish gray to dark dull red, and much divided by joints into rhomboidal 

 masses, mostly only one to two or three feet long. It is exposed upon a tract of four or five 

 acres, forming a picturesque little water-fall on a southern branch of Mound creek, and reaching 

 thence thirty rods or more to the east and south. The dip is about 5 S. In some places the 

 layers are obliquely laminated, this false bedding being partly steeper to the south, and partly, in 

 other places, level or slightly inclined northward. 



Over this rock the streamlet falls about thirty feet, its descent for the last twenty feet being 

 vertical, into a pool some four rods in diameter. Two rods east of this water-fall is a little gorge 

 or canyon, cut in the quartzyte 6 to 10 feet wide and 20 feet deep, with vertical walls, extend- 

 ing about forty rods southeasterly in the solid rock, marking the place of an older water-fall, 

 now diverted. About ten rods west of the principal fall is another interesting gorge perhaps 

 twenty rods long, reaching from north to south. This rock also forms conspicuous ledges be- 

 side Mound creek an eighth and a fourth of a mile north of this water-fall; and less than a mile 

 to the west, in the N. E. J of section 36, Germantown, in Cottonwood county, it makes a still more 

 interesting cascade and canyon on another of the head-streams of this creek. 



Cretaceous beds. In western Redwood county wells occasionally have 

 gone through the drift and passed into clay or shale below, apparently of 

 Cretaceous age, and sometimes proved so by the enclosed fossils. Such 

 sections are reported at Walnut Grove in North Hero township, and in 

 T. 111, R. 38, as described on a following page, in the list of wells illus- 

 trating the glacial drift. 



Cretaceous strata doubtless lie next below the drift upon the greater 

 part of this district; but their only outcrops, excepting within the Minne- 

 sota valley and the gorge of the Redwood river, occur on the Cottonwood 



river in Brown county. 



The first discovery of lignite, or brown coal, on the Cottonwood river was made in 1861 by 

 John F. and Daniel Burns, of Burnstown, in its north bank, near the northeast corner of section 



