436 THE GEOLOGY OF MINNESOTA. 



[Cretaceous beds. 



ceous age. The layers of clay are mostly white, but sometimes red; and the sand and gravel are 

 occasionally cemented with iron ore. Above these the bluff consists of till, and rises to a bight 

 about 150 feet above the river. 



A sandstone, which may belong to either the Jordan or St. Peter formations of the Lower 

 Magnesian group, but seems quite likely to be Cretaceous, and other beds more certainly referred 

 to this later age, occur in the banks of the Watonwan river at Garden City, southwest and north 

 of the fair-ground, rising fifteen to thirty feet above the river. Of these deposits Prof. Wiiichell 

 writes*: " It [the sandstone] is here associated with more or less clay, crag, and iron and lime 

 cement. A heavy deposit of drift crag [cemented gravel, probably Cretaceous] may be seen on 



E. T. Norton's place, and also opposite Mr. Norton's. Under the crag is clean 



white sand. A little further up in the bluff is red and blue clay, belonging, undoubtedly, to the 

 Cretaceous. This crag is sometimes made up of this white sand cemented, with little gravel. 



It lies in a continuous layer along the bluff, and projects like a bed of rock, the 



incoherency of the underlying white sand causing it to crumble out. This is also shown on the 

 north side [of the fair-ground], along the bluff where the current of the river has kept the surface 

 fresh. This sandstone is again exposed in the banks of the river about two miles above Garden 

 City." 



On the Le Sueur river close above the railroad bridge the Jordan sandstone, described on 

 page 428, is overlain by about sixty feet of clay and sa:;d or sandrock layers, irregularly inter- 

 stratified. In the lower portion the clay is mostly white, but at one place is red and by being 

 washed down paints a portion of the bluff a few feet in width. This is about a hundred feet 

 southeast of "chalk run," a gap in the bluff which has its name in allusion to these white and red 

 clays. The sand is mostly ferruginous, and is cemented by iron-rust. These beds rise from 

 thirty to forty feet above the railroad bridge, which is 825 feet above the sea. The clay which is 

 used at Mankato for the manufacture of pottery is obtained at this place, southeast of the railroad 

 and about fifteen feet above the level of the railroad grade. In the bank four rods east of the 

 railroad bridge, the following descending section was noted. It is embraced in No. 2 of 

 Prof. Winchell's general section already given. 



Section of Cretaceous beds near the Le Sueur river railroad bridge, sec. 35, Mankato. 



1. Coarsely rocky drift 4-10 ft. 



2. Stratified gravel and sand, ferruginous, farther eastward iron-cemented . . . 3-5 ft. 

 8. Dull gray, horizonally stratified clay 1-2 ft. 



4. Dull gray, horizontally stratified sand 4 ft. 



5. Second layer of clay, like No. 3 1 j-2 ft. 



6. Second layer of sand, like No. 4 4 ft. 



7. Third layer of clay, like No. 3 1 j-2 ft. 



8. Third layer of sand, like No. 4, seen 1 ft. 



The top of the last of these layers is six feet above the railroad, and is higher than the, white 

 and red strata which overlie the Jordan sandstone in the adjacent river-bluff. At the iron bridge, 

 about a half mile farther up this river, the Jordan sandstone is overlain by twenty feet of clayey 

 and sandy, nearly levelly stratified Cretaceous strata, of gray and whitish color, in many portions 

 containing small lumps of white clay. In the east part of section 2, Rapidan, the northeast bank 

 of the Le Sueur river shows a few feet of Jordan sandstone at the base, on which rest white and 

 gray Cretaceous clays, closely like the deposits which fill cavities of the Shakopee limestone in 

 South Bend and Mankato, nearly horizontal in stratification, having a thickness of twenty to 

 twenty-five feet and exposed along a distance of about twenty-five rods. These strata are reddish 

 in a few small and inconspicuous portions. Above them the upper part of the bluff is drift. 

 Again, an eighth of a mile farther south, Cretaceous strata of similar character form the bank on 

 the southwest side of this river along a distance of nearly twenty rods, but at the time of obser- 

 vation were much obscured by falling down. This blnff is 40 to 75 feet high, with ascent toward 

 the south, all above 30 to 40 feet being drift. 



On the Maple river are numerous exposures of sand or sandstone and clay, which closely 



Second annual report, p. lit. 



