The boulders were usually standing detached on the ground near the edge of the water, but sometimes they were heaped together in a pile in the middle of the pond. Upon an examination of the positions of the strange aggregations of stones which had been moved from their original place in the north to this plateau, the impression was conveyed to the mind that these smaller boulders may have been dropped during the period when icebergs were floating over the land. It seemed to be probable that some of the icebergs were stranded, and had left on these spots the cargo they had carried away from higher latitudes. Upon other parts of the level prairie where the land was dry, there were many isolated masses standing up in their places upon the surface, in the same manner as the Spirit rock near Mendota. It was remarkable that these boulders, which were often very large, were not embedded in the soil, but appeared to have remained in the positions in which they had been deposited. Some of the larger ponds contain quantities of wild aquatic plants, which yield a kind of rice—the same which was frequently mentioned by the French exploring missionaries in the seventeenth century—by the name of La Folle Avoine. This wild rice was gathered by the Dakotas and Chippewas, and stored by them for food in time of scarcity. As we approached the boundaries of North Iowa, we found that the winter had set in earlier than usual, and the prairies were covered with several inches of snow. The aspect of the country, upon which the only marks of life were the footprints of animals, was exceedingly desolate. The horizon was sharply defined by the white edges of the land against the sky, and the curvature of the earth was thereby made distinct. The land seemed to fall away from the eye at a distance which looked very near. On plains of this perfectly level character in these latitudes, the actual true distance of the horizon—as seen by a person of average height standing upon the ground—would be about three miles; but in consequence of the conditions of light upon the surface of the snow, it appeared to be less, and the borders of the round line of horizon seemed to confine us within a small circle. This effect was particularly noticeable when the sun rose and touched the eastern parts of the curvature, the sky at that time in the morning being clear and cloudless. The weather became daily more severe, and at last we had to encounter a hard gale of wind from the north-west. Suddenly one afternoon, a sweeping snow storm overtook us, and in a few hours all vestiges of the track were lost. Our position became perilous, as nothing could be seen which would help us in the slightest degree as a guide, and enable us to steer a straight course. The sky was gloomy and dark with snow clouds, and the prairie was as bare as the open sea.