428 THE UEOLOGY OF MINNESOTA. 



jurtlan sandstone. 



bridge, in South Bend, which show both the sandstone and limestone, the former reaches about 

 50 feet above the river, being capped by 20 to 25 feet of the latter. In sections 29 and 31, South 

 Bend, this Jordan sandstone declines in hight from 50 to 40 feet; at Rapidan Rapids its hight is 

 30 feet; and beyond this its elevation above the river is diminished to only a few feet at its last 

 outcrops, in the east edge of Garden City township. By comparison with the descent of the river, 

 it appears that the top of the sandstone is nearly level in these exposures, having about the same 

 hight as at Minneopa falls and in Judson. All these outcrops have the ordinary characters of the 

 Jordan sandstone, being white or gray, soft and mostly friable, in horizontal beds from a few 

 inches to one or two feet thick. At the bend of this river, in the south edge of section 21, South 

 Bend, where this formation rises on the north side to a hight of about 50 feet and is overlain by 

 20 feet of Shakopee limestone, the upper part of the Jordan sandstone contains occasional flat- 

 tened masses, two or three inches long and an eighth to a fourth of an inch thick, of a white 

 powder, which when wet becomes a sticky paste. 



In the north bluff of the Blue Earth river, within a short distance above the bridge in sec- 

 tion 27, South Bend, and about three-quarters of a mile above the mouth of the Le Sueur river, 

 is the place where the Sisseton Indians, as stated by Featherstonhaugh, obtained a bluish green 

 pigment which was held in high esteem. Nicollet says: li lt is massive, somewhat plastic, emits 

 an argillaceous odor when breathed upon; color bluish green; easily scratched with the nail, when 

 formed into hardened balls. The acids have no action upon it; it is infusible before the blowpipe, 

 but loses its color and becomes brown. This color is due to the peroxide of iron" [otherwise com- 

 bined chemically until changed by the blowpipe flame], "which it contains in the proportion of 

 ten per cent, at least. It contains no potash, and but a small proportion of lime." This was 

 found in a shaly layer at the line of junction of the sandstone and limestone; but it occurred 

 here only in small amount, and had been nearly exhausted before the time of Featherstonhaugh 

 and Nicollet.* In our exploration it was carefully looked for, but nothing of this kind worthy of 

 note was seen. Somewhere in this neighborhood, either in the bluffs of the Blue Earth or Le 

 Sueur river, as much as four thousand pounds of a similar green or blue earth, perhaps from this 

 horizon of the Lower Magnesian, but more probably from the Cretaceous shales or clay common 

 in this region, being supposed to be an ore of copper, was gathered and shipped to France by Le 

 Sueur, in the years 1700 and 1701. Further reference to this subject will be found on a following 

 page, in the description of the Cretaceous deposits. From this earth, the location and nature of 

 which remain in some uncertainty, the name of the river and thence of the county is derived. 



On the Le Sueur river the Jordan sandstone is frequently exposed along a distance of one 

 and a half miles next above the bridge of the railroad from Mankato to Wells, in section 35, of 

 South Bend and Mankato, and section 2, Rapidan. In ascending the river the first of these out- 

 crops is found four miles southwest from Mankato, 'and about a half mile south from the site of 

 Red Jacket mill, which was recently burned. Here this sandstone forms a perpendicular bank 

 20 to 30 feet high and an eighth of a mile long, lying at the northeast side of the river next above 

 the railroad bridge. It is a levelly stratified, but often obliquely bedded, friable, white sandstone. 

 Its top here is 800 feet above the sea. Overlying it is a thickness of about 60 feet of irregularly 

 interbedded clay and sand, with ochery and iron-rusted layers, probably Cretaceous deposits, and 

 above these glacial drift forms the upper part of the bluff. The Jordan sandstone here presents 

 a notable peculiarity which has not been observed in its outcrops elsewhere, excepting at the point 

 before mentioned on the Blue Earth river. This is the existence of frequent cavities in the sand- 

 stone, filled with masses of white friable clay, as described by Prof. Winchell, ; 'about an inch in 

 diameter, usually flattened, or pointed, or edged, which if dry crumble to powder in the fingers, 

 revealing little or no grit, but which when wet are sticky and plastic." At the iron bridge, near 

 the south line of section 35, South Bend, about half a mile southeast from the last, this sandstone 

 rises vertically to a hight of about 20 feet in the bank on the west side of the river, and is overlain 

 by 20 feet of Cretaceous clay and sand, succeeded by 10 feet of somewhat ferruginous drift. 

 About a half mile farther southeast, on land of 0. Ilalberg, near the center of the east half of sec- 

 tion 2, Rapidan, a short ledge of Jordan sandstone rises 15 feet or more above the river in its 

 southwest bank; and the opposite bank, at 20 to 40 rods up stream from the last, shows this rock 

 to a bight of 6 or 8 feet, overlain by 20 to 25 feet of Cretaceous clays, and capped by drift, the 



See historical notes respecting this locality, pp. 60 and 72; and of Le Sueur's copper mine, pp. 16, 5', and 71. 



