276 THE EARTH'S CRUST. [ms. 



direction through or along a rigid and at the same time an 

 elastic body like steel, provided it has the form of a plate 

 moving in or on media not of sufficient resistance to interfere 

 materially with the play of the plate, as it would be with the 

 crust of the earth, with the atmosphere on one side and a fluid 

 nucleus on the other. But I cannot understand the transmis- 

 sion of a rolling motion and the production of great transverse 

 fissures without the actual movement, as you would have in the 

 shaking of a carpet, of the whole mass of the crust affected by 

 the disturbance. 



Admitting that Sir William Thomson's investigations estab- 

 lished great rigidity as a whole, it still appears to me that there 

 must be fluid remnants at no great depth, although the central 

 nucleus as well as the outer crust are solidified. I certainly 

 understand from Mallet's description, and the account of others, 

 that although the movement or shock is vertical in places, that 

 in others it is one from side to side. 



No hypothesis, it seems to me, meets all the conditions of 

 geological phenomena so well (or if it meets [them] all) as that 

 of the original fluidity of the globe, and I would think that none 

 meets the present condition of volcanic and earthquake dis- 

 turbances so well as that the solidification is not yet thoroughly 

 complete, though the remaining quantity of fluid matter is not 

 such as to interfere with the rigidity required by Sir W. T. 

 to answer his determined conditions. This, in fact, is very 

 much the hypothesis of Mr Hopkins, but I should hesitate to 

 accept the thickness he assigns to the external crust. I would 

 refer earthquakes to that cause which has ever been affecting 

 the crust of the earth the incessant readjustment to a con- 

 tracting nucleus, however small that contraction may have 

 become. 



I saw Hughes 1 yesterday, and heard of the Barnwell dis- 

 covery. I hope he will accompany Evans and myself this 

 Easter to some of the French caves. I am sorry to hear your 

 armchair has such a hold of you, but trust it will become less 

 fixed as summer advances ; and with our united kind regards, I 

 am, sincerely yours, Jos. PHESTWICH. 



1 Woodwardian Professor of Geology, Cambridge. 



