426 THE GEOLOGY OF MINNESOTA. 



[Jordan sandstone. 



Wincliell says of this: " The beds are four to eight inches, although the uppermost three or four 

 feet of the quarry are very much weathered and in thinner beds. The bedding planes are usually 

 entirely covered with a green coating, and the body of the whole is specked thickly, and some- 

 times largely made up of green particles." 



The Jordan sandstone directly and conformably overlies the St. Law- 

 rence formation, but their contact has not been observed in Blue Earth 

 county. From the waterfall mentioned in section 12, Judson, this sand- 

 stone, gray or white, sometimes stained in small portions with iron-rust, 

 soft and often friable, has many exposures eastward along the Minnesota 

 valley, and also in the valleys of the Blue Earth and Le Sueur rivers. 



In going southeast from this waterfall the road soon rises about 75 feet to a terrace of modi- 

 fied drift, upon which it runs one and one-fourth miles to a wind-mill in the N. E. } of section 18, 

 South Bend, where this terrace is called " Wind-mill bluff." Next the toad descends to a terrace 

 of the Jordan sandstone, which is frequently exposed upon a width that varies from an eighth to 

 a fourth of a mile thro it gh a distance of two and a half miles east-southeast to South Bend, its 

 bight above the river being about 100 feet. The beautiful Minneopa falls, in the N. W. \ of 

 section 21, South Bend, four miles west of Mankato. have been produced by the excavation of 

 Lyons creek in this sandstone which here contaii s hard layers near its top, but is soft below, 

 being readily undermined by the waterfall and crumbled by weathering. The brink of this fall 

 is about 95 feet, and the highest exposure of the rock here about 110 feet above the river, these 

 hights being 850 and 865 feet above the sea. 



Of Minneopa falls Prof. Winchell writes*: " The perpendicular fall of the water is about 30 

 feet, but 45 feet of the sandstone can be made out. Before reaching the point where the water 

 leaps over r the stream works its way through a perpendicular thickness of 15 feet of sandstone 

 beds. It then comes in contact with a harder portion of the 'sandstone, which has a thickness of 

 about six feet. This resists the water longer than the underlying layers, and maintains a pro- 

 jecting shelf. The mist that ris. s keeps the walls wet, and the freezing of winter crumbles away 

 the soft sandstone, so as to form about the pool where the water strikes, a walled amphitheater 

 rising about 40 feet on each side. This glen is more or less shaded with elms, cedars, birches, 

 butternuts and oaks. It is prolonged in the form of a rough and shaded gorge, worn in the solid 

 rock, of about the same depth, down to the point of issue of the stream upon the Minnesota 

 bottoms, the distance of about half a mile. The gorge below the fall is darkened by the dense 

 foliage, Ihe stream in its course being much of the time hid from sight but for a few rods. This 

 gorge is crossed, about a quarter of a mile below the falls, by the St. Paul and Sioux City rail- 

 road. At the foot of the falls a little lake of water is confined by the upheaved pebbles in front 

 of the cascade. The gravel of the surrounding beach is hard enough to admit of a passage on all 

 sides. There are also several narrow paths along the walls of the amphitheater, where the fallen 

 fragments are sufficiently turfed and overgrown to permit a passage up or down the stream. An 

 elm tree which is nearly three feet in diameter grows near the foot of the cascade, and on the 

 right bank. Its annual rings of growth would indicate at least some part of the time elapsed 

 since the retreat of the fall from the place where it stands. Within six feet of it the perpen- 

 dicular sandstone wall rises to the bight of over forty feet. The stream is subject to great 

 fluctuations of volume, sometimes becoming quite dry. In passing down the Minneopa gorge to 

 its union with the Minnesota river, the bluffs become more and more wooded, the slone only 

 showing alternately in patches on opposite sides, and no lower view of the Jordan sandstone can 

 be had, at least none that can be proved to be lower." 



The unnamed waterfall in the N. W. j of section 12, Judson, three and a half miles north- 

 west from Minneopa, has also been described by Prof. Winchell.f "A little creek, which is dry in 

 summer time, exposes first about two feet of coarse sandstone in its bed. Following the creek 



'Second annual report, p. ISO. t dame, p. 152. 



