686 NOTES TO BOOK XVIII. 



in order to distribute the loose masses, yet still the work 

 appears to be beyond the possible effect of ordinary marine 

 currents, or any movements which would be occasioned by 

 a slow and gradual rising of the center of distribution. 



It has been suggested that a sudden rise of the center 

 of distribution would cause a motion in the surrounding 

 ocean sufficient to produce such an effect: and in con- 

 firmation of this, reference has been made to Mr. Scott 

 RusselFs investigations with respect to waves, already 

 referred to in Note (CA), vol. n. (Book vm.) The wave 

 in this case would be the wave of translation, in which the 

 motion of the water is as great at the bottom as at the 

 top ; and it has hence been asserted that by paroxysmal 

 elevations of 100 or 200 feet, a current of 25 or 30 miles 

 an hour might be accounted for. But I think it has 

 not been sufficiently noted that at each point this " cur- 

 rent 1 ' is transient : it lasts only while the wave is passing 

 over the point, and therefore it would only either carry a 

 single mass the whole way with its own velocity, or move 

 through a short distance a series of masses over which it 

 successively passed. It does not appear, therefore, that 

 we have here a complete account of the transport of a 

 collection of materials, in which each part is transferred 

 through great distances : except, indeed, we were to sup- 

 pose a numerous succession of paroxysmal elevations. 

 Such a battery might, by successive shocks, transmitting 

 their force through the water, diffuse the fragments of the 

 central mass over any area, however wide. 



The fact that the erratic blocks are found to rest on 

 the lower drift, is well explained by supposing the latter to 

 have been spread on the sea bottom while rock-bearing ice 

 masses floated on the surface till they deposited their lading. 



