ON THE UPPER MISSISSIPPI. 



499 



base of the hills. At " Old Man's Prairie," a measurement of the elevation of the 

 bluff gave a height of three hundred and fifty feet, the upper fifty feet consisting of 

 transported gravel, sand, and boulders, below which the Lower Magnesian Limestone 

 is the only rock visible, if we except a seam of sandstone at the base, two and a 

 half inches in thickness. The superior beds are intersected by numerous fissures, 

 which intersect the strata in all directions. 



At La Grange Mountain, near the head of Lake Pepin, is an interesting exposure 

 of the Lower Sandstone and Lower Magnesian Limestone. The whole height of the 

 bluff is about three hundred and fifty feet, of which the Lower Magnesian Lime- 

 stone constitutes one hundred and eighty-five feet. The section at this point is 

 given below : 







Feet. 



1. 



Soft green and yellow sandstone, containing Lingulas and Orhiculas, 



26 



2. 



Alternations of green and yellow sandstone, and schistose sandstone, 







with green particles disseminated, ..... 



5 



o 

 O. 



Brown dolomitic layers, containing Orthis, Lingulas, and columns* of 







Crinoidece, ........ 



4 



4. 



Brown, white, and green sandstone, with schistose dolomitic intercala- 







tions, ........ 



26 



5. 



Yellow and ash-coloured argillo-calcareous rock, containing Dikeloce- 







phalus Minnesotensis, Lingulas, and Orhiculas, 



4 



6. 



Alternations of brown and yellow sandstones, surmounted by thick-bedded 







white and brown sandstone, ...... 



50 



7. 



Slope covered with soil and vegetation, about .... 



135 



8. 



Lower Magnesian Limestone, F. 2, 



150 







400 



From this locality to one mile below the mouth of the Miniskah River, the 

 Lower Magnesian Limestone appears in perpendicular walls, forming the upper 

 portions of most of the bluffs. 



The next good section showing the members at the junction of these two forma- 

 tions, is about two miles below the head of Lake Pepin, and at Maiden's Rock. 



At the first of these localities, yellow and green sandstone is seen twenty-five 

 feet above the level of the lake ; and extending up the slope are thicker beds of 

 white and brown sandstones, supporting F. 2. 



About two hundred feet of a perpendicular escarpment of Lower Magnesian 

 Limestone faces the lake at Maiden's Rock, with a talus beneath of nearly the 

 same height, from which beds of sandstone occasionally appear. 



* The presence of the remains of Encrinites, in bed No. 3 of this section, is interesting, since hitherto 

 this family of fossils has never been observed before in this country, so low in the geological formations ; 

 the strata in which they occur being in beds equivalent in age to the Potsdam sandstone of New York. 

 The oldest Crinoids that we had any knowledge of previous to this discovery, are described by Hall in 

 the first volume of the " Paleontology of New York," and procured from the Chazy Limestone. 



Bed No. 4 contains the same remarkable species of Trilobite, Likeloccphalus Minnesotensis, first found 

 in argillo-calcareous beds on the banks of Lake St. Croix. Associated with this species at La Grange 

 Mountain, the cephalothorax and pygidium of another smaller species of Trilobite occurs, which will pro- 

 bably constitute a distinct genus. The same bed contains two species of Lingulas, one of which is pro- 

 bably peculiar to it. 



