484 



DESCRIPTION OF THE COUNTRY BORDERING 



4. Scam of grayish oolitic chert, with a thin incrustation of whitish decom- 



posing chert, . . . . . . . 2 to 3 



5. Light salmon-coloured magnesian limestone, with dendritic markings, 



and cavities lined with crystals of calcareous spar, in layers from 

 a few inches to two feet in thickness, containing Lingulne, Orthis, 

 and Trilobites, ....... 11 



The magnesian limestone at this locality does not differ essentially in appearance 

 from that noticed near Abert's Run.* It contains two kinds of Linguke ; one, an 

 elegant little species, of an ovate shape, with fine concentric striae, is not distin- 

 guishable from Lingula Dacotaensis, a form which characterizes the Lower Magne- 

 sian Limestone, at the quarry near Stillwater, and other localities throughout the 

 Chippewa Land District ; the other, of which we obtained only a few fragments, is 

 much larger, but the specimens are so imperfect, that the characters of the species 

 cannot be made out. Associated with these Lingulie, we found the cast of a small 

 Orthis, with fine radiating stride, and portions of the cephalothorax of a Trilobite, 

 related to the family Olenidce. 



Between White Rock and Traverse des Sioux, the land is high and rolling, and, 

 in general, well timbered with elm, oak, hard and soft maple, white and black 

 walnut, ash, and linden. The banks of the river are, usually, from eight to ten 

 feet high. 



Boulders, chiefly of granite, syenite, and porphyritic and greenstone trap, occur 

 in great profusion, scattered over the surface of the upland prairie, but we did not 

 notice any exposures of stratified rocks. The Lower Sandstone, F. 1, doubtless 

 forms the nucleus of the hills, since, in digging a well at Traverse des Sioux, near 

 the house of the Rev. Mr. Hopkins, thirty feet above the river, this rock was struck 

 a few feet below the surface. And one mile beyond Traverse des Sioux, the same 

 sandstone appears in the bed of the river. The rock is rather fine-grained, of a 

 light buff colour, and has numerous brown spots disseminated. It is more compact 

 than the sandstone occurring at White Rock. One of the layers is highly charged 

 with casts of Euomphalus Minnesotensis. 



Two miles above Traverse des Sioux, the sandstone exhibits a nearly perpendi- 

 cular face of twenty feet, towards the river ; and two miles still further up it forms 

 solid ledges, twenty-five feet thick, capped with twenty feet of magnesian limestone. 

 In the sandstone we found with the above Euomphalus, the pygidium of a small 

 Trilobite, but the rock was of such a friable character, that we were not able to pre- 

 serve specimens. The magnesian limestone contains Lingula Dacotaensis, and 

 remains of a species of Trilobite, apparently identical with that occurring at White 

 Rock. We could not perceive any dip in the strata at this section. 



* The composition of this magnesian limestone is as follows : 



Carbonate of lime, ....... 58-65 



Carbonate of magnesia, ...... 29-15 



Insoluble matter, ....... 7-25 



Alumina, oxide of iron, and manganese, .... 1-55 



Water, ........ 2-65 



Loss, ........ 0-75 



100-00 



