APPENDIX. 331 



and value of this tributary have particularly impressed every 

 member of the party. Its position as the central point of the 

 Sioux power, and its border position to the Chippewas, the repre- 

 sentative tribe of the great Algonquin flimily, render it now a 

 place of note, which fully justifies the policy of the department in 

 establishing a military post at the confluence of the river ; and 

 the importance cannot soon pass away, in the progress of the set- 

 tlement of the Mississippi Yallcy.* It is the great route of com- 

 munication with the valley of the Red River of the North, and 

 the agricultural and trading^ settlements of Lord Selkirk in that 

 fertile valley, and its complete exploration by a public officer is 

 desirable, if not demanded.f 



Of its geological character but little is known, and that con- 

 nects it with both the great formations which have been noticed 

 as succeeding each other at the great Peace Rock. That the 

 granitical formation reaches it at a high point is probable, from 

 the large reported boulders. The Indians bring from the blue 

 earth fork of it, one of their most esteemed green and blue argilla- 

 ceous pigments, of which the coloring matter appears to be car- 

 bonate of copper. They also bring from the Coteau des Prairie, 

 probably Carver's "shining mountains," specimens of that fine 

 and beautiful red pipe stone, which has so long been known to be 

 used by them for that purpose. This mineral is fissile, and mode- 

 rately hard, which renders it fit for their peculiar ripe sculptures. 

 I found small masses of native copper in the drift stratum at the 

 mouth of this stream, on the top of the cliffs on the Mississippi, 

 opposite the mouth of the St. Peter's. 



Crystalline Sand Rock. — This stratum reveals the same 

 crystalline structure which is so remarkable in the sandstone 

 caves, near the Potosi road, in the county of St. Genevieve, 

 Missouri ; and the sand obtained from it, like that mineral, would 

 probably fuse, with alkali, in a moderate heat, and constitute an 

 excellent material for the manufacture of glass. It is also, like 

 the Missouri sandstone, cavernous. In both situations, these 

 caves appear to be due to water escaping through fissures of the 

 rock, where its cohesion is feeble, carr3nug it away grain by grain. 



* Thirty years bas made it the centre of the new territory of Minnesota, which 

 has now entered on the career of nations. 



J This object was accomplished by an expedition by Major L. Long, in 1823. 



