On Scratches produced by Icebergs, 9?* 



some authors that glacier ice is most plastic when most charged 

 with water, and the lower part of an iceberg must be water-logged. 

 Again, a glacier, for instance of 1000 feet in thickness, must 

 press on its bed with the whole immense weight of the super- 

 incumbent ice; but in an iceberg 1000 feet thick, as the whole 

 floats, there will of course be no pressure on a surface exactly 

 level with its bottom, and if driven over a prominence standing 

 up at the bottom of the sea some 50 or 100 feet above the basal 

 line of the berg, only the weight of as much ice as is forced up 

 above the natural level of the floating mass, will press on the 

 prominence. It may therefore, I think, be concluded that an ice- 

 berg could be driven over great inequalities of surface easier than 

 could a glacier. That the weight of a comparatively thin sheet of 

 ice is sufficient to groove rocks, we may infer fi'om the case de- 

 scribed by Sir C. Lyell of the scores made by the packed shore-ice 

 on the coast of the United States. That icebergs do not break up 

 when grounded, as a priori might have seemed probable, is ob- 

 vious from the simple fact of their having been often observed 

 in this condition in open turbulent seas. Let anyone who has 

 witnessed the crash of even so small an object as a ship, when 

 run into by another having only a barely perceptible movement, 

 reflect on the terrific momentum of an iceberg, some mile or two 

 square, and from 1000 to 2000 feet in thickness, when, borne 

 onwards by a current of only half a mile per hour, it runs on a 

 submarine bank : may we not feel almost certain, that, moulding 

 itself like a glacier (of which it originally was a portion), but 

 owing to its water-logged state and little downward pressure 

 moulding itself more perfectly than a glacier, it would slide straight 

 onwards over considerable inequalities, scratching and grooving 

 the undulatory surface in long, straight lines ? In short, if in our 

 mind^s eye we look at an iceberg, not as a rigid body (as has 

 hitherto been always my case) which would be deflected or broken 

 up when driven against any submarine obstacle, but as a huge 

 semi-viscid, or at least flexible mass floating on the water, I be- 

 lieve much of the difficulty will be removed which some have 

 experienced in understanding how rectilinear grooves could be 

 formed continuously running, as if regardless of the outline of 

 the surface, up and down moderately steep inequalities, now ex- 

 isting as hills on the land. It should be borne in mind that the 

 course of deeply-floating icebergs is determined by the currents 

 of the sea, and not, as remarked by Scoresby, by the shifting 

 winds ; and as the currents of the sea are well known to be defi- 

 nite in their course, so will be the grooves formed by current- 

 borne icebergs. It is indeed difficult to imagine any difference 

 between the effect on the underlying surface, of a glacier pro- 

 pelled by its gravity, and that of a mountainous island of ice 



