ON THE UPPER MISSISSIPPL 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 fect. The section at this point is 
given below : 
Feet. 
1. Soft green and yellow sandstone, containing Lingulas and Orbiculas, . 26 
2. Alternations of green and yellow sandstone, and schistose sandstone, 
with green particles disseminated, _. : ‘ ; . 5 
3. Brown dolomitic layers, containing Orthis, Lingulas, and columns* of 
Crinoidew, . c : : ‘ : : : 4 
4. Brown, white, and green sandstone, with schistose dolomitic intercala- 
tions, : ‘ ‘ , : ‘ : i 26 
9. Yellow and ash-coloured argillo-calcareous rock, containing D¢keloce- 
phalus Minnesotensis, Lingulas, and Orbiculas, , P 4 + 
§. Alternations of brown and yellow sandstones, surmounted by thick-bedded 
white and brown sandstone, . : i : ; : 50 
7. Slope covered with soil and vegetation, about. ’ d 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 “ Palzontology of New York,” and procured from the Chazy Limestone. 
Bed No. 4 contains the same remarkable species of Trilobite, Dikelocephalus Minnesotensis, first found 
in argillo-caleareous 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. 
