LAKE PEPIN.--This sheet commends itself to notice by its extent and picturesque features. It is an expansion of the river, about twenty-four miles long, and two or three wide. Both its borders and bed reveal the drift stratum, and the observer recognizes here, boulders of the peculiar stratification which has, in ancient periods, characterized the high plateaux about the sources of the river. Such are its hornblendic, sienite, quartz, trap, and amygdaloid pebbles, and that variety of the quartz family which assumes the form of the agate and other kindred species. Moved as these materials are annually, lower and lower, by the impetus of the stream, other supplies, it may be inferred, are still furnished by the shifting sand and gravel bars from above. The mass must submit to considerable abrasion by this change, and the diminished size of the drifted masses become a sort of measure of the distance at which they are found from their parent beds. CHIPPEWA RIVER.--This stream is the first to bring in a vast mass of moving sand. Its volume of water is large, which it gathers from the high diluvial plains that spread southwest of the Porcupine Mountains, and about the sources of the Wisconsin, the Montreal, and the St. Croix Rivers, with which it originates. TROMPELDO (_Le Montaine des Tromps d'Eaux_).--This island mountain stands as if to dispute the passage of the Mississippi, whose channel it divides into two portions. Distinct from its height, which appears to correspond with the contiguous cliffs, and in the large amount of fresh debris at its base, it presents nothing peculiar in its geology. PAINTED ROCK.--This vicinity is chiefly noted for its large and fine specimens of fresh-water shells. WISCONSIN.--Like the Chippewa, this stream brings down in its floods, vast quantities of loose sand, which tend to the formation of bars and temporary islands. It originates in the same elevated plains, and bespeaks a considerable area at its sources, which must be arid. It is a region, however, in which lakes and rice lands abound, and it may, in this respect, be geologically of the same formation as the higher plateaux of the Mississippi, above the Sandy Lake summit. Its sides produce many species to enrich our fresh-water Conchology.