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

624 ADDENDA. fessor Hitchcock (Report on the Geolog. of Massachusetts, p. 167) de- scribes a tract about two hundred miles in width, over which nearly all the bare rock on the hills, even to the height of three thousand feet, is scored by parallel lines. In some parts boulders, weighing from fifty to one hundred tons, are yet lying on the surfaces, which bear the marks of their passage. The furrows are generally directed a little west of north, but in the western part of Massachusetts, and in the eastern of New York, they extend in a north-west and south-east line, and in one part even to W. 20° N. M. Sefstrom and Professor Hitchcock explain these appear- ances in their respective countries by the same agency, as Sir James Hall does in Scotland. The theory of a great debacle is in these cases based on the united presence of erratic boulders, ridges of waterworn materials, forming tails to scarped hills, and parallel furrows and scratches on the surface of the rocks. 1st. With respect to the boulders, it would be superfluous to repeat the arguments in favour of the idea of their transportation by ice : and in the case of Sweden, it would be pre-eminently superfluous, as we know (see Lyell on the Rising of the Land in Sweden, Phil. Transact., 1835) that blocks are there transported yearly by this means. 2d. Every one who has examined a great estuary, or a channel where the tides run strongly, is aware that linear banks are formed behind any obstacle. Tlierefore these tails of diluvium might have been formed, as far as regards their external form, by ordinary means ; and with respect to their internal structure, which appears extremely irregular, and without any stratification, it must be difficult for any one to speak with certainty, until the joint efifects of ice transporting coarse fragments and gentle currents of water, fine mud, are better known. Mr, Lyell, indeed {Phil. Transact.^ 1835, p. 15) has advanced strong reasons, showing from the structure and com- position of the oasars that they could not have been formed by any sud- den debacle. Whilst such linear banks were depositing on one side of the hills, the other, or exposed front, would almost necessarily become scarped. 3d. We have the admission of Sir James Hall, that the scoopings and grooves resemble those produced by the slow action of running water therefore the scratches appear to be the only part of the phenomenon which remains unexplained. In tlie Alps, we are told, that scratches are formed on rocks by glaciers grinding over them. According to the theory of floating ice, we have evidence in the erratic blocks near Edinburgh, that ice was formerly in action there ; and, from the analogies given in this volume, it might well have been so, since the scene of supposed action lies two degrees nearer the Pole than Georgia, in the southern ocean, " almost wholly covered with everlasting snow." VVhat tlien would be the effect of the tides and gales of wind, driving packed icebergs with irresistible force, through chan-