We had been travelling on a slightly curved line from Chicago to the spot, in the latitude of 41° 52´ 20´´, and had now reached a point where the course tends more directly to the northeast and north. By the best accounts, the length of Lake Michigan, lying directly from south to north, is four hundred miles. There is no other lake in America, north or south, which traverses so many degrees of latitude, and we had reason to expect its flora and fauna to denote some striking changes. We had passed down its west, or Wisconsin shore, from Sturgeon Bay, finding it to present a clear margin of forest, with many good harbors, and a fertile, gently undulating surface. But we were now to encounter another cast of scenery. It is manifest, from a survey of the eastern shore of this lake, that the prevalent winds are from the west and northwest, for they have cast up vast sand dunes along the coast, which give it an arid appearance. These dunes are, however, but a hem on the fertile prairie lands, not extending more than half a mile or more, and thus masking the fertile lands. Water, in the shape of lagoons, is often accumulated behind these sand-banks, and the force of the winds is such as to choke and sometimes entirely shut up the mouth of its rivers. We had found this hem of sand-hills extending around the southern shore of the lake from the vicinity of Chicago, and soon found that it gave an appearance of sterility to the country that it by no means merited. On reaching the mouth of St. Joseph's River (3d), a full exemplification of this striking effect of the lake action was exhibited. This is one of the largest rivers of the peninsula, running for more than a hundred and twenty miles through a succession of rich plains and prairies; yet its mouth, which carries a large volume of water into the lake, is rendered difficult of entrance to vessels, and its lake-borders are loaded with drifts of shifting sand. The next day's journey carried us fifty miles; and, on proceeding ten miles further on the 4th, we reached the mouth of the Kalamazoo.[140] Before reaching this river, I discovered on the beach a body of detached orbicular masses of the calcareous marl called septaria--the ludus helmontii of the old mineralogists. On breaking some of these masses, they disclosed small crystalline seams of sulphuret of zinc. The Kalamazoo irrigates a fine tract of the most fertile and beautiful prairies of Michigan, which, at the date of the revision of this journal, is studded with flourishing towns and villages.