92 



but has a continuous forward motion during the whole transit of the 

 AA'ave's length. A complete transposition does therefore result from 

 the wave-transit ; and the wave of translation, says Mr. Scott Russell, 

 may be regarded as a mechanical agent for tlie transmission of power 

 as complete and perfect, as the lever or the inclined plane. 



Arguing from these remarkable data of Mr. Scott Russell, and 

 applying them to our geological plmsnoniena, Mr. Hopkins states, 

 that currents of twenty-tive and thirty miles an hour may be easily 

 accounted for, if repetitions of elevations of from 160 to 200 feet be 

 granted ; and with motive powers producing a repetition of such 

 waves, our author has no difficulty in transporting to great distances 

 masses of rock of larger dimensions than any boulders in the North 

 of England. 



In bringing his mathematical and mechanical knowledge to bear 

 on this difficult question, Mr. Hopkins has rendered essential service 

 to geologists, well convinced, as they must be, that no one cause 

 could have been adequate to the formation of all the varieties of 

 superficial detritus. He has in sliort arrived at numerical results, 

 acquainting us with the exact influence of the moving power, under 

 certain conditions*. 



Admitting with Mr. Hopkins, tliat nearly all the great boulders 

 at a distance from the mountains from whence they were derived, 

 were accumulated upon the bottom of the sea, which bottom Avas 

 subsequently elevated, I regret, that whilst he allows the possi- 

 bility of floating ice having played a part in some cases in the 

 transport of large blocks, he should doubt its agency in the 

 country under consideration ; for the North of England is 

 full of examples of far-borne detritus, the position of which 

 seems to me inexplicable by calling in the poAver of water 

 alone. Many practical geologists must, I think, admit, that in 

 the desiccation of the former bed of the ocean, and in its conversion 

 into our present lands, the submarine outline of hill and dale has 

 been, to a gi'eat extent, preserved ; and if this be granted, no 

 waves of translation nor any force of water can have hurled blocks 

 across high ridges and deep valleys Avhich are transverse to the 

 direction which the erratics have taken, and of such relations 

 England offers numerous examples. To a remarkable instance 

 of this transport in our central counties I formerly adverted, con- 

 tending that without the agency of floating icebergs the phacnomenon 

 seemed inexplicable-]-, and I now direct your notice to an excellent 

 example of this nature which was communicated by Mr. Clay at 

 the last meeting of the British Association, who shows that in the 

 narrow valley of the Calder excavated in the carboniferous strata, 

 there is a group of boulders of granite and other crystalline rocks, 

 of which there are no traces in any part of the adjacent country. 

 As these blocks are separated from the Cumbrian chain by the lofty 

 region of Lancashire, and numerous deep, transversal or east and 



* See Proc. Gool. Soc> vol. iii. p. 766. See also a hypothesis by the present 

 Masterof Trinity Coll. Cambridge, on this subject, Silurian System, p. 538. 

 t Silurian System, p. 035 et scq. 



