[229] Thirty years has made it the centre of the new territory of Minnesota, which has now entered on the career of nations. [230] This object was accomplished by an expedition by Major L. Long, in 1823. Of its geological character but little is known, and that connects 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 argillaceous pigments, of which the coloring matter appears to be carbonate 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 moderately 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, carrying it away grain by grain. In stopping at one of these caves, about twelve miles below St. Peter's, we found this cause of structure verified by a lively spring and pond of limpid water flowing out of it. VALLEY OF THE ST. CROIX.--This river originates in an elevated range of the elder sand and pebble drift, which lies on the summit between the Mississippi system of formations, and the Lake Superior basin. It communicates with the Brulé, which is "Goddard's River" of Carver, and with the Mauvaise or Bad River of that basin. Specimens of native copper have been found on Snake River, one of its tributaries.[231] [231] This river was explored by me in 1831 and 1832, in two separate expeditions in the public service, accounts of which have been published in 1831 and 1832, of which abstracts are given in the preceding pages. GEOLOGICAL MONUMENTS.--In descending the river for the distance of about one hundred miles below St. Anthony's Falls, my attention was arrested, on visiting the high grounds, by a species of natural monuments, which appear as if made by human hands seen at a distance, but appear to be the results of the degradation and wasting away, on the Huttonian theory, of all but these, probably harder, portions of the strata.