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

620 ADDENDA. is caused by the passage of the ice or of the pebbles.* Althougii the ice- bergs 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 cur- rents 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 marked 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 they were detached ; and as the winds and currents generally have suffi- cient 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 genernlly\ landed on the shores of the chan- * It must be remembered, that I am here considering the effect of ice- bergs, 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 scored. 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. -j- We might expect that they would sometimes be launched into the deep, whilst on their passage. M. Charpentier (Edinburgh 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 vallei/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 several fragments lying near one ano- ther." 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.