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Show 620 'ADDENDA. is caused by the passage of the ice or of the pebbles."* Although the iccbergs might be drifted from side to side of the sound, if they were moved after having grounded, it would be along the shore by the set of the currents or wind, and perhaps slightly up and down by the tidal changes. Would not the necessary effect of this be, that the scratches formed by the sand grating between the rocks and the bottom of the icebergs should be, with some irregularities, longitudinal, or (from the effect of the tidal movement) oblique? And as the mountains slowly emerged during ages, every part would be thus acted on; and consequently the whole surface would be ma,rked by longitudinal scratches. The icebergs on the South American coast sometimes transport angular fragments of rock, to the distance of many miles from the glacier whence thry were detached ; and as the winds and currents generally have sufficient steadiness to drive any floating object soon on shore, (as is known to be the case with a capsized boat, a barrel, or floating carcass, &c.), so the blocks of rock would be generallyf landed on the shores of the chan- "* It must be remembered, that I am here considering the effect of icebergs, in inland and protected sounds. Dr. Richardson tells me, that the great icebergs in the Arctic sea are packed together, and are driven with such force against the shore, that they push up before them, to the height of several feet, every pebble and boulder which lies on the bottom ; and consequently the submarine ledges of rock are kept absolutely bare. If a fragment were to be wedged beneath one of these mountain-masses of ice, when forced upward with such overwhelming power, it is impossible to doubt that the underlying surface of solid rock would be deeply scot·ed. As it is known that the shingle on most beaches has a tendency to travel in one direction, so must the icebergs; and hence we may conjecture, that the grooves, would generally be slightly oblique to the line of coast, and parallel to each other. t We might expect that they would sometimes be launched into the deep, whilst on their passage. M. Charpentier ( Edinbu1-gll New Phil. Journal, vol. xxi., p. 217) observes, speaking of another theory, "This view is equally insufficient to account for the extraordinary position of immense single blocks, which we sometimes find planted vertically in the soil, in the valle:;s, as on the sides of a mountain, and split up throughout their whole extent from top to bottom,-a phenomenon which would force us to believe that these blocks, had fallen perpendicularly from a certain height on the very spots where we now see them, and had been rent asunder by the fall, into the sev~ral fragments lying near one another." M. Charpentier considers this owing to the fragments· having fallen through fissures in the enormous glaciers, which, as he believes, extended from the Alps, across the lake of Geneva, and up the Jura. The explana· tion above suggested is, at least, as simple as this. ADDENDA. 621 nels between the Alpine ranges, and not dropped in the intervening spaces. If any pointed rock came so near the surface that a floating mass of ice . thus charged, grounded on it, the block would, when the ice melted, be there left. But it may be asked, would the blocks usually be deposited on the bare surface of the rocky bottom off the shore, or on an intervening layer of gravel or sediment ? From what I have observed when passing in boats through the channels of Tierra del Fuego, and from frequent examinations of the armings of the lead used in sounding, I feel neady sure that absolutely bm·e submarine rock is not very common. Moreover, where matter is depositing near a shore, the finer th~ particles are, the further they are drifted : in approaching a coast I have actually traced ever:; step in the series, from the fine.st sand to large pebbles. But as the land in any case is slowly elevated, the same forces which carried the large pebbles to a certain distance from the beach, and the smaller ones to a still further distance, will, after each little elevation, carry them somewhat further :-a layer of little pebbles thus covering the sand, and a layer of large pebbles the smaller ones. Hence, when the part near the shore is converted into dry land, a section of the bed which was originally the bottom of the sea will necessarily show solid rock covered by sand, this by fine pebbles, and these again by others, gradually increasing in size. Such then, I conclude, must have been the nature of the sublittoral deposits of the Alps, during their assumed slow elevation. Finally, as icebergs of large size would seldom be driven up on the beach of a sheet of water, if, like the channel between the Jura and the Alps, it '\'ere protected from the open sea, any fragments of rock transported by them would have been dropped some way outside, and therefore when upraised with the whole country, they would be found in most cases reposing on beds (where the loose matter had not been subsequently removed), characterized by the order of superposition just described. Such is the explanation I would suggest of the very curious facts observed by M. Agassiz. I make no assumptions which are not supported by strong analogies and the foundation of the theory-namely, a change of climate of a peculiar kind-can be shown by reasoning, independent of the existence of erratic blocks, to be probable in a high degree : whether this is the case with the theory of M. Agassiz, I leave the reader to decide. Having said thus much on the scratched rocks of the Alps, I am tempted to make a few remarks on those of Scotland, described by Sir James Hall"* in his celebrated paper (Edinburgh Pili!. Transact., vol. vii.) *' Sir James Hall believes that erratic boulders were transported by debacles, when embedded in ice. He seems to have been led to this opinion, by a clear perception of the difficulty of supposing the existence |