Dr. Gr. J. Stoney on Denudation and Deposition. 563 



movements within the earth, do not interfere. In the case 

 of submarine deposits they must, being buoyed up by the 

 water, have a specific gravity either approaching or ex- 

 ceeding 3, to be competent to occasion a deepening of the 

 ocean. If the deposit has less specific gravity it tends to 

 make the ocean shallower. The general result is that denu- 

 dation everywhere tends to make the land part of the surface 

 of the earth to rise, inasmuch as denudation always removes 

 matter with a specific gravity greater than 2 ; whereas under 

 water some of the deposits tend to make the ocean deeper and 

 others tend to make it shallower. 



12. Some of the events to be accounted for are the fol- 

 lowing : — The surface of the solid earth partly projects above 

 the ocean in the form of continents and is partly submerged. 

 Denudation has been going on for ages over those parts that 

 project ; while deposition of heavy materials (see ' Challenger ' 

 Eeport) has with equal persistency been going on over pre- 

 cisely those portions of the floor of the ocean which are in the 

 present day the most submerged. Not only so, but denudation 

 has, as a rule, been going on for ages more rapidly over the 

 parts which are now the most elevated above the sea, and less 

 rapidly over the parts which are less elevated. What I desire 

 to insist on, and what I think has been proved and is certain^ 

 is that it is physically possible that what were originally less 

 elevations and depressions may have been intensified as time 

 went on, by the denudations and depositions which have 

 invariably accompanied them ; and 1 venture to express the 

 opinion that it is largely through this agency (in fact every- 

 where except where it has been counteracted by other factors) 

 that the elevations and depressions which we now find upon 

 the earth, have attained their present magnitude. If Dr. Chree 

 will weigh the fact that this is physically possible, he w ill 

 hardly I think continue to maintain the paradox that the 

 elevations and depressions have become what they now are, 

 not in consequence of the agencies we find persistently in 

 operation, but in spite of them. 



13. In his first paragraph, p. 494, Dr. Chree describes it 

 as " legitimate to hold that the deep-seated material has had 

 its elasticity, so to speak, l killed ' under the enormous pres- 

 sure to which it is exposed ; ' ; and in his third paragraph he 

 gives as his opinion that the only satisfactory alternative " is 

 to treat the earth as incompressible, or very nearly incom- 

 pressible, throughout all but the surface strata/' Of these 

 alternatives I have endeavoured to show in paragraph 4 of the 

 present paper, that the former is physically impossible, and 

 in paragraphs 3 and 4 that there is no presumption in favour 

 of the second alternative. 



