LE SUEUR COUNTY. (537 



Jordan sandstone and Shakopee limestone.] 



easily eroded sandstone. These formations are nearly horizontal in strati- 

 fication and mainly conformable with each other; as if in the same sea, 

 with no evidence of important change in level or in the relations of land 

 and sea, the deposition of sandstone, after having formed a stratum fifty 

 feet or more in thickness over a large area, was succeeded by the formation 

 of an equally extensive and thicker stratum of magnesiau limestone. 



The Jordan sandstone is white or light gray, excepting small portions where it is stained 

 by infiltrating ferruginous waters. In texture it varies from a fine-grained to a coarse-grained 

 deposit, and rarely encloses small pebbles. Nearly all its material is quartz, the particles of 

 which are mostly rounded by water- wearing. When exposed to the air in dry situations, it be- 

 comes harder and more firmly cemented than in its natural bed, where it is so friable that it can 

 be excavated by a shovel and pick. Its name is from Jordan in Scott county, where this forma- 

 tion is well exhibited and has been considerably used as a building stone. 



The overlying Shakokee limestone, so named from the town where it is best exposed in 

 Scott county, is a hard, buff-colored, mostly thick-bedded, in many portions siliceous and cherty, 

 magnesian limestone or dolomyte. The whole thickness of this formation in Le Sueur county 

 was apparently from 50 to 75 feet or more, but only its lower 10 to 25 feet remain in the outcrops 

 of Le Sueur county. 



The terrace of these strata in Kasota is from one to one and a half miles wide. It is about 

 75 feet above the river, and extends eight miles from Kasota to Mankato, its northern half , four 

 miles long, being in Le Sueur county. On its surface is generally spread a coarse, water-worn 

 gravel, from one to five feet thick, holding multitudes of rock-fragments of all sizes up to one 

 foot in diameter, chiefly derived from the limestone which forms the terrace. In some places, 

 also, it is sprinkled with boulders, mainly of granite, gneiss, and schists, of all sizes up to five 

 feet in diameter and rarely larger. The railroad well at Kasota station went through drift, 

 mostly limestone gravel, 8 feet; solid limestone, 21 feet, and sandstone, 6 feet. Here and gen- 

 erally in this vicinity, the base of the limestone is approximately 40 feet above the river; but it 

 sinks to about half this hight in going one and a half miles northward in Saint Peter, from the 

 railroad bridge to the highway bridge. 



Ottawa is situated on another terrace, one and a half miles long and three-fourths of a mile 

 wide, composed of the same formations of limestone and sandstone. Their junction in the bluff 

 near Charles Schwartz's limekiln is about 45 feet above the river. The terrace generally rises 

 20 or 25 feet higher, which is about the average depth remaining of the limestone. 



In both these formations fossils are usually absent; but they occur numerously in some 

 layers of each at a few localities. Dr. B. F. Shumard, who assisted Owen, reports that in out- 

 crops of the sandstone a mile above Traverse des Sioux, in the bed of the Minnesota river near 

 its most eastern bend in the north part of Kasota, "one of the layers is highly charged with casts 

 of Euomphalus Minnesotensis." He also found this gasteropod and the pygidium of a small trilo- 

 bite at Kasota in this sandstone in the river-banks. The cliff formed by these strata beside the 

 Minnesota river at Ottawa is called by Dr. Shumard the White Bock bluff. Its hight is stated 

 to be 72 feet, the base being concealed by a talus to the hight of 30 to 40 feet, above which are 

 in ascending order, "white and brown sandstone, composed of rounded, rather coarse, semi- 

 transparent grains of quartz, loosely cemented, 20 feet; green siliceous earth, 1 foot; seam of 

 grayish oolitic chert, with a thin incrustation of whitish decomposing chert, 2 to 3 inches; light 

 salmon-colored magnesian limestone, with dendritic markings, and cavities lined with crystals of 

 calcareous spar, in layers from a few inches to two feet in thickness, containing Lingulce, Orthis, 

 and trilobites, 1 1 feet. The magnesian limestone at this locality .... contains two kinds 

 of Lingulce; one, an elegant little species, of an ovate shape, with fine concentric striae, is not 

 distinguishable from Lingula Dacotaensis,a. form which characterizes the Lower Magnesian lime- 

 stone, at the quarry near Stillwater, and other localities throughout the Chippewa Land District; 

 the other, of which we obtained only a few fragments, is much larger, but the specimens are so 

 imperfect that the characters of the species cannot be made out. Associated with these Linyidce, 



