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

Ci22 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, ^d Series, 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, sandstone 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, tlie 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 Jordanliill, 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 Reliqui<B DiiuviaiKe, 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 almost always seen marked by long linear scratches."