About three miles above the mouth of the river, we landed at a Chippewa village. While exchanging the usual salutations with them, we noticed the children of an African, who had intermarried with this tribe. These children were the third in descent from Bongo, a freed man of a former British commanding officer at the Island of Michilimackinac. They possessed as black skins as the father, a fact which may be accounted for by observing, what I afterwards learned, that the marriages were, in the case of the grandfather and father, with the pure Indian, and not with Africano-Algonquin blood; so that there had been no direct advance in the genealogical line. The St. Louis River discharges a large volume of water, and is destined hereafter to be a port of entry for the lake shipping, but at present it has shoals of sand at its mouth which would bar the entrance of large vessels. Proceeding up the river, we found it very serpentine, and abounding in aquatic plants, portions of it yielding the wild rice. At the computed distance of twenty-four miles, we reached the establishment of the American Fur Company. It was seven o'clock when we came to the place, where we encamped. Lake Superior is called by the Chippewas a sea. The superficial area of the lake has been computed by Mr. Darby at a little under nine hundred billions of feet, and its depth at nine hundred feet. By the latest surveys and estimate, the altitude of Lake Superior above tide water, is about six hundred and forty feet.[62] Allowing Mr. Darby's computation to be correct, this would sink its bed far below the surface of the Atlantic. [62] _Vide_ Appendix. This lake has been the theatre of very extensive volcanic action. Vast dykes of trap traverse its northern shores. One of the principal of these has apparently extended across its bed, from northeast to southwest, to the long peninsula of Keweena, producing at the same time, the elevated range of the Okaug Mountains. One of the most remarkable features of these dykes is the numerous and extensive veins of native copper which characterize them. Subsequent convulsions, and the demolition of these ancient dykes, by storms and tempests, have scattered along its shores abundant evidence of the metal and its ores and veinstones, which have attracted notice from the earliest time. The geology of its southern coasts may be glanced at, and inferred, from the subjoined outlines. [Illustration: Geological outline of Lake Superior.]