x8o». EVOLUTION OF OCEANS AND CONTINENTS. 513 



Restorative or Catastrophic Change, must be our principle of inter- 

 pretation. 



Here, however, it may be objected that Mr. Fisher has supported 

 the theory of the permanence of oceans, and that he assigns to the 

 sub-oceanic crust a structure which differs from that of the continental 

 crust. In his Appendix, however, he has partially altered his con- 

 ception of the structure of the sub-oceanic crust, and he has recently 

 read a paper before the Cambridge Philosophical Society in which he 

 arrives at results which tell strongly against his speculation about the 

 origin of ocean basins ; in this I much rejoice, for that chapter in his 

 book had never commended itself to me. 



It must be remembered, too, that Mr. Fisher has not attempted 

 to enter into the history of the sub-oceanic crust. His position is 

 simply this ; his calculations show that, if his hypothesis be true, 

 there are large tracts of crust which must have the special structure 

 he ascribes to them ; he does not assert that they have always had 

 that structure, but he does see a difficulty in supposing that, having 

 acquired that structure, they can ever again become continental land. 



A. J. Jukes-Browne. 



2 L 



