94 Correspondence — Mr. Arthur Vaughan. 



volume due to pressure, but upon the transference of material," etc. 

 I never did rely on decrease of volume, as Mr. Eeade will see if he 

 reads my original article more carefully, whereas, again and again, 

 I insisted upon the main principle of transference of material. 



Further on I I'ead, that Mr. Reade has found out that the 

 maximum elevation which could possibly be produced, according 

 to my theory, is 1000 feet. Absurd though I believe this I'esult to be, 

 from my own calculations, I shall be most grateful if he will indicate 

 his method of analysis, as the problem seems to present exceptional 

 mathematical difficulties. Looking at the question in its simplest 

 aspect the analysis employed must take account of each of the 

 following phenomena : — 



(1) The gradual contraction of a spherical cap with the consequent 

 production of tension at its boundaries and frictional stress beneath. 



(2) The inbending of the crust, and consequent outshear of 

 material from beneath, with the necessary production of frictional 

 stress. For this outsheared material must set up tensions and com- 

 pressions in the superincumbent crust ; the tensions being directed 

 from the centre of the area outwards, and the compressions pro- 

 ducing folding and ridging, principally at the boundaries, in the 

 regions immediately preceding those of iipheaval. 



(3) The rate of contraction beneath the area, which will neces- 

 sarily be made more rapid by the extension of material, and the 

 consequent exposure of hotter layers to the cooling influence. 



In fact, we have to deal with elevation due to distortion of the 

 inner nucleus, and this cannot be limited to the amount by which 

 the suboceanic shell can contract ; for the viscous stresses due to 

 outshear of subjacent material will compress the bounding parts of 

 the area into folds and ridges. The only rough limit which can be 

 assigned is, that the volume of the elevations above sea-level cannot 

 exceed the volume of the ocean. 



Another objection which my critic urges is that, since my theory 

 demands that the surrounding continental crust should yield to the 

 intrusion of rock underneath, the area could not bend inwards, 

 because it has no anchorage. Here he has totally neglected the 

 friction beneath the sinking area, arising from the outshear of 

 material, which it seems to me will be powerful enough, not only to 

 hold the area, but to fold and ridge its boundaries. 



Lastly, Mr. Reade seems to argue that, granted the anchorage, 

 the tension of rock would not be sufficient to allow of enough 

 pressure to produce any tending inwards. In this reasoning he 

 has entirely omitted the vastly important time factor ; for, in 

 reasoning on all geological phenomena, the length of time available 

 is the most important point in the problem ; since there are few 

 geologists who will not grant that the making of a mountain range 

 is spread over a vast number of years. 



Now, it is well known that any practically solid body, acted upon 

 by differential stresses, however small, will yield to their influence, 

 if the time be sufficiently prolonged. Hence there is no need for 

 the tension to exceed or even approach the breaking tension of steel. 



