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Show 622 ADDENDA. on the Revolutions of the Earth's Surface :-a case which has always appeared to me to be the strongest ever adduced in favour of the theory of an overwhelming debacle having rushed, at least in that country, over hill and valley. The furrows and scratches in the same district are parallel to each other, and hence run in the same direction :-thus, near Edinburgh, they extend in a line a little north of west and south of east, that is parallel to the valley of the estuary ; but both to the eastward and westward they deviate from this line by more than half a right angle ; and on the south-west part of Scotland they have no uniform direction. In the north of Scotland, however, near Brora, Mr. Murchison (Geolog. Transact. 2d Se1ies, vol. ii., p. 357) found the hills marked in parallel lines, directed north-west and south-east. The furrows and scratches near Edinburgh seem generally to traverse the less inclined surfaces, but Sir James, speaking of one part, says "the perpendicular face as well as the rest is covered with lines, which are horizontal, or nearly so." In these respects the case appears very similar to that of the Alps : the rocks, however, are not polished ;'*' but this may be owing to their nature, s:mdstone and trap, and not to any difference in the cause; for Dr. Richardson tells me that in the same rivers in North America, in which the granitic rocks are much polished, those of laminated limestone are not at all so. Near Edinburgh, where the lines extend west and east, the western face of the hills (of which the highest mentioned is four hundred and seventy feet above the sea) is chiefly marked, whilst on the opposite or protected side, a long tail of (so called) diluvium extends, which consists of blue clay, with large erratic boulders embedded in it. These boulders, as I am informed by Mr. James Hall, and by Mr. Smith of Jordanhill, are themselves marked with parallel lines, having one direction, which shows that they were held fast whilst drifted across the country, and not rolled over and over, like a pebble in a stream.. It is of glaciers in the Alps and in other regions of central Europe, excepting at great altitudes ; and from such situations a debacle was absolutely requisite to transport fragments on ice. Sir James rejects the belief of M. Wrede (given on the authority of De Luc), that the boulders of the Baltic may have been brought into their present place by ice, acting, during a steady and slow change in the level of the ocean. M. Wrede, therefore, appears to have been the originator of the theory advocated in this volume ; and no country was more likely than Sweden to have given birth to such a theory. '* It is, however, said ' in Professor Buckland's Reliquice Diluviance, p. 202, that Colonel Imrie found the surface of some trap-rocks in the southern parts of Stirlingshire, having "a considerable degree of polish; and this polish is afmost always seen marked by long linear scratches." ADDENDA. 623 admitted by all that the grooves on the solid rock were formed by the passage of these boulders over it. Although the minor inequalities of the surface of the land appear to have had no influence whatever on the action which produced the scratches, yet the larger features, as the general bearing of the main valleys, appear to have determined their directiOn. Sir James distinctly states that the scoopings and furrows have precisely that form which the long action of torrents tend£ to produce on a solid rock ; but he adds, and I believe most truly, that the furrowed surface produced by such means is smooth, and not deeply scored and scratched. It is indeed utterly inconceivable that large stones should be carried along as if " independently of tlteil· gravity" by any ordinary means, with such velocity, as to mark with horizontal lines the perpendiculm· face of a rock. From these facts,-from the presence of great erratic blocks, from the steepness of one face of the grooved hills, and the tail of sediment stretching out from the other, Sir James Hall, having in his mind the recot"ded cases of the great waves consequent on earthquakes, inferred that a vast deluge had burst over the country from the westward. M .. Brongniart, and lately M. Sefstrorn (L'Institut, Febmm-y 22d, 1837), have described phenomena in Sweden almost identical with those of Scotland. The rocks are there grooved and scratched,"* even to the height of 1500 feet, in north and south lines, parallel to the valley of the Baltic and of the Gulf of Bothnia ; but they are considerably tdeflected by the larger inequalities of surface. The north side of the hills are most affected, whilst from the southern side, long ridges, called oa.wrs, stretch out ; they arc composed of sand and waterworn materials, and appear to be similar, but on a much larger scale, to the tails of diluviurn in Scotland. In Sweden, however, the erratic blocks always lie on the surface of these ridges, and are not embedded within tQem : but M. Sefstrom says, that at the time when the grooves were formed, enormous masses of rock were torn from the mountains. In the United States, the phenomenon of the grooved rocks appears to be developed in an extraordinary manner. Pro- '* Mr. Lyell, moreover, describes (Pltilosoplt. Transact., 1835, p. 18), the rocks of gneiss on the beach near Oregrund in Sweden, as being so " smooth and polished, that it is difficult to walk on them." Further on (p. 21 ), he describes the large bodies of ice, which are annually packed on this coast, so as to be eighteen feet thick : here then we have the same phenomena as in the Alps; and great icebergs in movement, instead of solid glaciers. More lately M. Berzelius has sent specimens of these rocks, "polished as if by emery in a constant rt:ctilinear direction" ( Edinb. New Phil. Journal, vol. 1., p. 313), to Paris, accompanied by a Jetter to M. Elie de Beaumont. |
