MR MILNE ON THE GEOLOGY OF ROXBURGHSHIRE. 483 



But whilst I think it fair to notice these circumstances, as creating in my 

 mind some difficulty in understanding how an earthquake- wave can transport 

 boulders, I admit that the opinion of such mathematicians as Mr HOPKINS and Mr 

 SCOTT RUSSELL, who concur in ascribing a transporting power to such a wave, is 

 deserving of all reliance. The views of the former I have already stated ; and to 

 shew the views of the latter gentleman, I may be allowed to quote the following 

 passages from a correspondence I have had with him on the subject. " The valu- 

 able application," says Mr RUSSELL, " which Mr HOPKINS has made of our know- 

 ledge of the laws of the great wave of translation, is in perfect accordance with 

 all the phenomena I have examined in my observations on this class of waves. 

 In the first place, Mr HOPKINS' mode of genesis of the wave, is identical with a 

 method of genesis which I have adopted in experiment, viz., the upheaval of a 

 considerable surface on the bottom of the channel. Suppose a depth of ocean of 

 400 feet : then, according to my experiments, the velocity of transmission of the 

 wave would be 77 miles an hour. But if the wave were of a height of 50 feet 

 above this level, the velocity of the wave would be increased to 84 miles an hour. 

 The velocity of translation of such a wave could attain a maximum of 27 miles 

 an hour. This represents the current of the particles of water tending to move 

 an obstacle at the moment when the highest part of the wave is passing." " It 

 is perhaps important to observe, that the transporting power of such a wave will 

 be greatly facilitated by encountering a gradual shallowing and contracting of 

 the firth or channel into which it enters, as in the case (viz. the granite boulders 

 of Liddesdale) which you have applied this force to explain. 



" There is an additional view of this subject I may suggest to you, viz., that 

 on a hard or rocky surface, the chances are much in favour of the large block. 

 The tendency to crush an opposing obstacle, increases with the weight, or is as 2 6 ; 

 this being of a given size, both for the little and the large boulder. Further, there 

 is a gain of moving force, which is as the distance from the centre of gravity of 

 the block from the obstacle. This again gives us an increased chance in favour 

 of the large block as 2 : 1. Hence, on hard ground, the chances of motion, and 

 of continuing in motion, are greatly in favour of the large block." 



On writing Mr SCOTT RUSSELL, to suggest whether his wave of translation, 

 though it should move the block, would not then pass and leave it behind, I re- 

 ceived an answer from which I quote the following passage : " I see some diffi- 

 culty in getting the large boulder into motion, but little in keeping it going, after 

 it has set out. If you start it by a gentle slope, then the water would have no- 

 thing to do but give it way. A hard and tolerably even bottom, like a level strati- 

 fied rock, would greatly facilitate the locomotion ; and as to its being bedded in 

 mud or earth, why, the rushing of the waters past the boulder would soon clear 

 that away. Besides, the presence of a column of water, or a wave 20 feet high, 

 would be more than equal to the whole weight of such a boulder as you describe ; 



