MR MILNE ON THE GEOLOGY OF ROXBURGHSHIRE. 431 



of waters from the westward, which bared most of the hills on that side, leaving 

 or depositing on their opposite or lee sides, vast accumulations of sand and gravel, 

 containing, in many cases, large fragments of rocks. 



The question, then, is, could such a rush of waters have transported from 

 Criffel to Liddesdale the rounded boulders, some of them 3 or 4 tons in weight, 

 which are now to be seen there ? 



In answering this question, I refer to the Geological Manual* of Sir HENRY 

 DE LA BECHE, for the following facts, which are the more valuable, as not ad- 

 duced by him in support of any theory, but are given merely as illustrations of 

 the power of water to move heavy bodies. He says, that at " Plymouth, during 

 the severe gales of November 1824, and also of the commencement of 1829, blocks 

 of limestone and granite, from 2 to 5 tons in weight, were washed about on the 

 Breakwater like pebbles : about 300 tons, in blocks of these dimensions, being 

 carried a distance of 200 feet, and up the inclined plane of the Breakwater. A 

 block of limestone weighing 7 tons was washed round the western extremity of 

 the Breakwater, and carried 150 feet. Two or three blocks of this size were 

 washed about." I may be permitted to add, that, having visited Plymouth a 

 few months ago, I was shewn by Mr STEWART, who has charge of the Break- 

 water, several blocks, from 7 to 10 tons in weight, which, in the storm of January 

 last, had been moved from 15 to 20 yards. 



These effects of aqueous action become less surprising, when it is considered 

 that a granite block of 5 tons weight in air, weighs only about 3 tons in salt water ; 

 and, moreover, that the power of a current to move a solid body increases as the 

 square of its velocity. So that, as Mr HOPKINS has observed in a paper recently 

 read by him in the Geological Society, " if a current of ten miles an hour would 

 move a block of 5 tons, a current of twenty miles an hour might, under similar 

 circumstances, move one of 320 tons." Mr HOPKINS, in the paper just alluded to, 

 has given an account of the boulders in Yorkshire, which have been transported 

 from Cumberland, and has adverted to the different theories by which that trans- 

 port is accounted for. He gives it as his opinion that these boulders, as well as the 

 whole mass of diluvium with which they were associated, were transported whilst 

 the country was under sea ; an opinion which I had myself very confidently em- 

 braced and advocated, long before I had heard of Mr HOPKINS' views. He explains 

 in his paper, not only the efficacy of currents of a given velocity to move and 

 transport blocks, but the mode in which such currents may have been produced ; 

 and, finally, he does not " hesitate to affirm the entire adequacy of such a cause 

 to transport all the erratic blocks derived from the Cumbrian mountains, and 

 therefore to conclude, that such has been the agency by which that transport has 

 actually been effected." 



* Page 82. 

 VOL. XV. PART III. . 6 O 



