564 Dr. Gr. J. Stone}' on Denudation and Deposition. 



14. Finally, Dr. Chree thinks that the result arrived at by 

 calculating the amount of strain produced by applying a 

 normal force at one point of a plane bounding a theoretically 

 infinite elastic solid, devoid of plasticity and without weight, 

 would give " a much better idea" than my method " of the 

 order of magnitude of the elastic effects due to denudation 

 and deposition " in the cases where the loaded area is limited 

 to some few thousands of square miles [say where it is an 

 area from 30 to 100 miles across] . Before this view can be 

 admitted, Dr. Chree will have to show that a force applied 

 at a point of the supposed surface would produce anything 

 like the same dynamical effect as a pressure applied over an 

 area so extensive that it behaves dynamically somewhat like 

 the upper surface of a girder from 80 to 100 miles in length. 

 He will also have to find some mass of non-volcanic mountains 

 of this extent, which stand upon materials devoid of the plas- 

 ticity, and not accompanied by the geological u faults," which 

 tend to isolate such mountain ranges and their " Hinterland" 

 from the neighbouring parts of the earth. My own obser- 

 vations lead me to suppose that no such case can be found. 



1 5. On the whole, it does not appear to me that Dr. Chree's 

 criticisms have shaken any of the positions that I ventured to 

 put forward. 



16. To put the whole matter briefly : — What I submit as 

 the outcome of a careful inquiry may be summarized as 

 follows — Whenever through the operation of any cause one 

 of the existing continents emerged however little above the 

 waters, denudation at once began to operate everywhere over 

 it, and has ever since persisted in producing upon it whatever 

 is the natural effect of denudation. So far is certain. It is 

 also certain that the removal from any large continental area 

 of a layer of such materials as exist at the surface of the earth 

 will either (1) raise the new surface above the old surface 

 or (2) will depress it*. A priori reasoning does not indicate 

 w T hich of these opposite effects should follow from the removal 

 of the load, viz., a stratum having a specific gravity between 

 2*25 and 3 ; because the issue depends not only on the known 

 factors (the thickness of the stratum and its weight), but also 

 on the compressibility and other physical properties of the 



* The fact that in a mountainous country denudation scoops out valleys 

 may suggest to the superficial observer that the essential effect of denu- 

 dation is to lower the surface. It is, however, certain that the mountain- 

 ran^ e, as a whole, will press less on the material beneath it in consequence 

 of the denudation which has scooped out its valleys ; that this under- 

 lying material down to unknown depths will in consequence expand ; and 

 that this expansion must somewhat raise the whole mountain-range. 



