BLUE EARTH COUNTY. 435 



Cretaceous beds.] 



that is sometimes as much as three inches thick. These old crevices cut across the strata and 

 pass from top to bottom of the formation. They are filled with the same, or a very similar, light- 

 colored clay, the same being continuous from the clay between the Shakopee and Jordan upward 

 through the openings to the top of the limestone strata, and there spreading out, in imperfectly 

 laminated beds, over the similarly rusted upper surface of the Shakopee. The bed of clay under 

 this limestone is known to extend back from the bluff of the river about eighty feet, and seems to 

 be in situ and of Cambrian age. Yet it seems not to be confined to this place between the Jordan 

 and Shakopee formations, where the most of it is seen; and as it occupies eroded cavities and all 

 seams and small openings within the Shakopee, and also overlies that formation, apparently 

 unconformably, it has been considered of Cretaceous age.* Prof. A. F. Bechdolt, of Mankato, 

 regards it as a result of chemical change in the overlying St. Peter sandstone and the underlying 

 Jordan sandstone; but it more probably resulted from a local degradation of the hydraulic Shak- 

 opee limestone, through long sub- aerial exposure, if its origin be at all attributable to such agents." 



"This white clay appears frequently at the same horizon, overlying the Jordan sandstone, 

 at points in the Le Sueur valley. It was examined on the land of S. F. Alberger, along the banks 

 of the Le Sueur in section 35, Mankato, where it lies about twenty feet above the river at the 

 railroad crossing, and is overlain by a series of confused, concretionary and lenticular beds of 

 sandstone, with alternations of clay, passing upward into a rusty conglomerate and crag-like 

 rock, and into a sandstone containing traces of wood, similar to that seen in Fillmore and Mower 

 counties, and at Fritz' quarry in Nicollet county, evidently of Cretaceous age. In ascending the 

 river from the railroad crossing, the water line rises over the underlying sandstone, and reaches 

 this clay bed. It is seen to become red in some places, and often somewhat gritty. The valley 

 of the Le Sueur in this vicinity, and its tributary valleys, also the deserted channel through In- 

 dian lake, to which Prof. Bechdolt has called attention, are wrought principally in Cretaceous 

 strata, overlain by a deposit of drift clay which shows, in numerous instances, the effect of water 

 in its deposition." 



Professor Winchell summarizes, in descending order, the following 



General section of the Cretaceous in the Le Sueur valley, sec. 35, Mankato. 



1. Conglomerate and sandstone; with traces of woody fiber; in oblique and lenticular 



stratification; the probable equivalent of fossiliferous strata at Fritz' quarry in 

 Nicollet county, and of the sandstone a few miles southwest of New Ulm 20-30 ft. 



2. Potter's clays and fine sand, irregularly and lenticularly interbedded 20-30 ft. 



3. Rusty and confused, concretionary sandrock 20-30 ft. 



4. White (kaolinic?) clay; within of a light greenish color; becoming red and arena- 



ceous in some places 6-8 ft. 



5. Jordan sandstone, seen 20 ft. 



Professor Bechdolt states that a slab of rusty sandstone was found some years ago on the 



bluff back of Mankato, containing fossil leaves resembling Salix; also, that a small shark's tooth 

 was picked up in the alluvium at the mouth of the Blue Earth river; and that at any time small 

 pieces of lignite coal may be found in the alluvium at the mouth of the Blue Earth, brought down 

 by the latest freshet from the valley. All these were doubtless derived from Cretaceous forma- 

 tions. 



On the Blue Earth river above the localities already mentioned, Cretaceous beds are reported 

 by Mr. John Leiberg in the left (north) bank of the river about twenty rods below the new bridge 

 in section 27, South Bend, being a somewhat sandy, deep green shale, exposed along an extent of 

 about a hundred and fifty feet, rising in a flattened anticlinal about five feet above the line of low 

 water; overlain by a bed of dark, ferruginous gravel, about ten feet thick, containing concretionary 

 iron ore (limonite 1 ; above which is light gray or white, friable sand or sandstone, about thirty feet 

 thick; succeeded by till, which forms the upper part of the bluff, f 



At the east end of the Rapidan Rapids bridge, the cliff of Jordan sandstone, thirty feet high, 

 is overlain by ten feet or more of interstratified clay, sand and fine gravel, referred to the Creta- 



Ihe second annual report, pp. 176 181; also the eighth annual report, p. 109. 

 tit seems quite likely that this is the site of Le Sueur's copper mine, as it agrees well with Penicaut'a dncriDtion 



17 nn H 42H1. 



*See 

 (See pages 17 and 428). 



