Captain Vetch on Icebergs, ^ % 57 



The agency of icebergs is not to be denied ; we see them at 

 work in the present day, and we can easily appreciate some of 

 their effects. But I would venture to caution geologists 

 against enlisting them to account for too many effects. I 

 well recollect, when attending your lectures, I was very much 

 surprised to find on the side of Dumpendcr Law a portion of 

 the clinkstone porphyry very nicely polished, as if done by a 

 lapidary. In those days the explanation was, that currents of 

 water had formerly passed at the heights of these polished 

 rocks, and bearing with them sand and gravel, which produced 

 a polish. Certainly the rarity of the occurrence was not very 

 conclusive, where so extensive and sweeping an agent was the 

 performer. With respect, however, to the case at Dumpender 

 Law, by frequently visiting the spot, I ascertained in a most 

 satisfactory manner the cause of the polish. I observed that 

 the sheep, in passing from one part of the hill to another, had 

 to pass the projecting polished rocks ; and farther, that the 

 passage was so narrow that they generally rubbed their fleece 

 on the face of the rock. Professor Leslie happened then to 

 be lecturing incidentally on the polish given to hard substances 

 from very minute and delicate materials, and he felt perfectly 

 convinced that the fleece of the sheep had been the polishing 

 substance. I have no doubt, however, were a modern Ice- 

 bergian to pass the spot on Dumpender Law, he would imme- 

 diately summon a mountain of ice to his assistance ! 



When I returned from Mexico in 1829, I stated to some 

 eminent geologists, that sweeping floods carrying sand and 

 gravel could not be admitted as a satisfactory explanation of 

 polished rocks; as I had examined, in Mexico, the beds of nu- 

 merous rivers cut out of the solid rock, and bearing vast quan- 

 tities of sand and gravel, and that in the dry season, when I 

 could examine every part of the bed, I had never detected a 

 striated polish, or indeed what could be considered a polish at 

 all, in the rocky beds. I was, however, told, that though the 

 torrents in Mexico might move with great force and velocity, 

 that nevertheless, if that was not sufficient to polish their beds, 

 currents of water might have existed, during certain changes 

 of the earth's condition, flowing with the velocity of a cannon- 

 fehot, 1000 miles an hour ; and with those who had such a 



