618 



ADDENDA. 



other facts (p. 381), are quite intelligible to me from the briefness, witli 

 which they are alluded to. M. Agassiz says (p. 375), " The erratic 

 blocks of the Jura every where repose on polished surfaces, all those at 

 least which have not been carried beyond the crest of our mountains, and 

 which have not fallen to the bottom of our longitudinal valleys, as may be 

 seen throughout the valleys of the Creux du Vent. But they do not 

 repose immediately upon these polished surfaces. Wherever the rounded 

 pebbles which accompany the great blocks have not been removed by 

 subsequent influences, it is remarked that small blocks, in other words 

 pebbles of different sizes, form a bed of some inches, and sometimes even 

 of many feet, upon which the great angular blocks repose. These pebbles 

 are also much rounded, even polished, and are heaped up in such a way 

 that the larger are above the smaller, and that the last often pass below 

 into a fine sand, lying immediately over the polished surfaces. This 

 order of superposition, which is constant, is opposed to all idea of a 

 transport by currents ; for in this latter case the order of the super- 

 position of the pebbles would have been precisely reversed." Further on 

 (p, 379) he remarks that the action of the glaciers is immense; for 

 these masses, continually moving upon each other, and on the surface, 

 bruise and grind down every thing moveable, and polish the solid surfaces 

 on which they repose ; at the same time that they push before them all 

 that they encounter, with a force which is irresistible. It is to these 

 movements (of the great stratum of ice) we must attribute the strange 

 superposition of the rolled pebbles, and of the sand, which immediately 

 reposes upon the polished surfaces ; and it is unquestionably to the 

 grating of this sand upon these surfaces that the fine lines which we find 

 (previously compared to the scratches made by a diamond on glass) are 

 owing, and which would never have existed, if the sand had been acted 

 upon by a current of water." Now it may be demanded, by what pos- 

 sible means can such violent action arrange the large pebbles above the 

 smaller ones, and these again above the sand? The fact appears to me 

 utterly inexplicable on this view. Again it is said, that the surface of 

 the rock is marked by furrows and gibbosities, as well as by scratches, and 

 that these " never follow the direction of the slope of the mountain, but 

 are oblique and longitudinal (that is, in the line of the mountain, and 

 therefore nearly horizontal), a direction which excludes every idea of a 

 stream of water being the cause of these erosions." What explanation 

 will it be believed is offered for this fact? — It is, that the fine lines and 

 furrows " must have resulted from the much greater facility which the ice 

 had in dilating itself in the direction of the great Swiss valley, than trans- 

 versely, confined as it were between the Jura and the Alps." ! 



