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Show 624 ADDENDA. fessor Hitchcock (Report on tlte Geolog. of Massachusetts, P· 167) describes a tract about two hundred miles in width, over which nearly a~l 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 Mas~achusetts, and in the eastern of New York, they extend in a north-west and south-east .line, and in ~ne part even to W. 20o N. M. Sefstrom and Professor Hitchcock explam 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. Ist. 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. Therefore 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 effects 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 composition of the oasars that they could not have been formed by any sudden 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 the Alps, we are told, that scratches are formed on rocks by glaciers grinding ovet· 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." What then would be the effect of the tides and gales of wind, driving packed icebergs with irresistible force, through chan- ADDENDA. 625 nels, and over rocky shoals ;-each part of the surface being exposed for centuries, as the country was elevated, to this action? Would not the fragments of rock embedded in the ice grate in a direct path over the surface, regardless of minor inequalities? and would not the fragments themselves be grooved and scored in one direction ? Can we for one moment believe it possible that boulders, either in water or in the thickest mud, could be driven over a rugged surface, or along a perpendicular face of solid rock, with such enormous velocity as with their points to groove and.scratch it, and nevertheless not to be rolled over and over, like a stone descending a mountain, but to be marked with parallel lines of abrasion, equally with the fixed, underlying mass? It appears to me that we assuredly can make no such admission. Travellers in the Arctic regions tell us that the drift-ice, with its irresistible power, can force up the gravel and sand into mounds (see Geogmph. Journal, vol. viii., p. 221), and drive before it great boulders, and even ships, and masses of ice, high and dry on the 'beach. What then would be the effect of a few pebbles, or a single fragment, between such masses of ice and a steep coast-wall of rock ? Would not scratches "horizontal, or nearly so" be formed, ''indicating (to use Sir James Hall's words) that grinders had been pressed against the rock;" as if" independently of their gravity''? In this explanation only verce causce are introduced, and reasons can be assigned, for the belief that these causes have been in action in these districts. On the theory of debacles, it still remains to be proved that rocks can be thus scooped and furrowed, or hills scarped; although I am far from affirming they cannot,-and scratched, I presume, they certainly would be. With respect to Sweden, where the land is now rising, and where ice even still is a transporting agent, it is undoubtedly the part of the geologist, to endeavour by long and laborious research to account for the phenomena by these real agencies. For to introduce, before it is absolutely forced on us, the hypothesis of a deluge of mud and stones, fifteen hundred feet deep in Sweden, or three thousand in North America, which rushing over the country, rounded the northern fronts of the hills, and rolling by their eastern and western flanks, left them marked with oblique furrows, is to violate, as it appears to me, every rule of inductive philosophy. Page 297. With reference to the embedment of the Siberian animals with their flesh, I have mentioned in a note, the case of ice described as risin" from the bottom of the sea, off the coast of Greenland. Messrs. Dea;e and Sim~son, during their late memorable journey along the shores of the Arcttc ocean, speaking of one part ( Geograph. Journal, vol. viii., p. 218) VOL. Ill. ~ Q** |
