Narrative of the surveying voyages of his majesty's ships Adventure and Beagle (vol.3)

614 ADDENDA. zones, tliat solid glaciers descend to the sea in low latitudes ; I might have added that it is in this same hemisphere, that the icebergs, which have been formed in the Polar Regions, are drifted furthest from their birth- place, liorsburgh f Philosoph. Transact., 1830) describes several great ice- bergs seen by a ship, in her passage to India, in 35° 50' S. : that is, far to the northward of the latitude, where tree-ferns, arborescent grasses, para- sitical orchideous plants, and even palm-trees grow ; and within sixty miles of the land, where the rhinoceros, elephant, hippopotamus, lion, and hyena, are very numerous. Page 289. Until lately I was not aware that there were sufficient data to speak with some precision of the soutliern limits of erratic blocks in the northern half of the New World. In Canada, and in the northern parts of the United States, innumerable great scattered fragments of rocks have been described by Bayfield, Bigsly, Hitchcock, and others. In parts of Massa- chusetts, according to Professor Hitchcock (Report on the Geology of J, boulders seem to cover the whole face of the country. Further south- ward we hear from Mr. Rogers {Sejjorl to Brit. Assoc, vol. iii.) that boulders are common over the great valley which crosses Pennsylvania, Maryland, and Virginia (lat. 36° 30' to 42°). and likewise in the states of Ohio, Kentucky, and Indiana, which are in nearly the same latitude. Mr. Rogers having described some blocks of sandstone at Washington and on the Susquehanna, which must have come from some distance northward, adds that " Drake in his picture of Cincinnati (39° 10') mentions large masses of granite in that part of the Ohio, resting on the ordinary finer diluvium. The nearest granite to the north is at least one hundred leagues distant; while no primary rock occurs south or east, within even a much greater limit." He then proceeds, " We are reminded here of the great detached blocks, which strew the plains of northern Europe, and the ex- planation suggested, that they have beta carried there upon floating ice ;" and concludes with the important remark, that Mr. Conrad, who has ex- plored the state of Alabama (30° to 33°) was never once able to perceive a boulder upon its surface. It would hence appear that 36° 30' is the southern limit of the dispersion of erratic blocks in the United States ; and these are spoken of, as having come from the north. Therefore, there is no occasion to suppose that the ice, in which by the theory they are believed to have been embedded, was formed in so low a latitude as that here mentioned ; and at present, in the southern hemisphere, icebergs are drifted to latitudes, though not formed in them, nearer the tropic than 36° 30'. In Europe I cannot hear of erratic blocks having been found further south than the southern flanks of the Alps, in lat. 45°; and Hum-