46 PROTOZOIC ROCKS 
A little below the Red Wing Village, near the northern extremity of Lake 
Pepin, is a remarkable headland, which has all the appearance of a hill split 
down the middle, as shown in the subjoined cut. Here the Lower Magnesian 
LA GRANGE MOUNTAIN. 
Limestone forms about one hundred and fifty feet of the upper portion of the hill. 
The base, for one hundred and eighty feet, is chiefly sandstone.* 
About thirteen miles below the mouth of the St. Croix, and two or three miles 
below the mouth of Vermilion River, back in the bluffs west of the Mississippi, the 
sandstone can no longer be seen, and the Lower Magnesian Limestone extends from 
the water level to the height of two hundred and thirty feet. Below the mouth 
of the St. Croix are low ledges only, of the same rocks, the whole height of the hill 
being about seventy feet, and immediately at the mouth the ledges are still lower.t 
Still ascending the stream, the strata take a local rise, so that three or four miles 
above the mouth of the St. Croix, the sandstone again emerges from beneath the 
water, and rises to the height of twelve to fifteen feet above low-water mark.§ It 
very soon sinks again, however, for, at Red Rock, there are only low ledges of 
Lower Magnesian Limestone, twelve feet thick.|| Not far beyond that locality, it 
disappears from the surface, so that, before reaching the town of St. Paul’s, it is 
replaced by the Upper White Sandstone, such as has been before noticed, in the 
section at Prairie du Chien, as occupying the slope above the terrace of Lower 
Magnesian Limestone. | | 
Between St. Paul’s and the New Cave, going up the stream, the strata dip from 
twenty-five to thirty feet per mile. Thence, still ascending, there is another local 
rise in the strata, about ten feet to the mile.** 
Connecting these and other observations, made along the Mississippi, between 
* See Sect. 1, M. + See Sect. 1, N. 
t See Sect. 3, and background to Sect. 5; also Sect. 1, O. 
§ See Sect. 1, P, and Sect. 5. || See Sect. 5, and Sect. 1, Q. 
J See Sect. 1, R. ** Sect. 5, and 1 T. 
