620 



ADDENDA. 



is caused by the passage of the ice or of the pebbles.* Although 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 ge7ieraUy\ 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. 



f We might expect that they would sometimes be launched into the 

 deep, whilst on their passage. M. Charpentier (Edinburgh New Phil. 

 Journaly 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 valleys, 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. 



