DRY LAKD IK GEOLOGY — COLEMAN. 271 



load much less complete, and also that they are carried out by slow 

 movements in the " asthenosphere " much below Hayford's level of 

 complete compensation at 76 miles below the surface. 



He would probably agree that on the broad scale continents are 

 buoyed up because they are light, and ocean bottoms are depressed 

 because the matter beneath them is heavy. He would admit that to 

 transform great areas of sea bottom into land it would be necessary 

 either to expand the rock beneath by several per cent or to replace 

 heavy rock, such as basalt, by lighter materials, such as granite. 

 There is no obvious way in which the rock beneath a sea bottom can 

 be expanded enough to lift it 20,000 feet, as would be necessary in 

 parts of the Indian Ocean, to form a Gondwana land; so one must 

 assume that light rocks replace heavy ones beneath a million square 

 miles of the ocean floor. Even with unlimited time, it is hard to 

 imagine a mechanism that could do the work, and no convincing 

 geological evidence can be brought forward to show that such a thing 

 ever took place. 



Discussing this question not long ago in the Journal of Geology, 

 Prof. Chamberlin showed that the only typical case of deep-sea 

 deposits found on land, the well known one of the Barbadoes, occurs 

 on one of the great hinge lines around which motions of the earth's 

 crust take place and has no real bearing on the change of ocean bot- 

 toms of continents.^ The same may be said of the deep-sea deposits 

 on Timor, in the East Indies, recently described by Molengraaff.^ 

 In position Timor is almost the counterpart of the Barbados in the 

 West Indies, 



The distribution of plants and animals should be arranged for by 

 other means than by the wholesale elevation of ocean beds to make 

 dry-land bridges for them. W. D. Matthew's excellent paper on 

 climate and evolution suggests ways in which this may be done more 

 economically. 



The elevation of mountain chains by folding or the overriding of 

 blocks might be expected to make trouble for the isostatic theory; but 

 the two best known examples, the Eockies and the Himalayas, seem 

 to be approximately in isostatic equilibrim. In the case of the Hima- 

 layas, the youngest and highest of the great mountain systems, it is 

 staggering to find nummulitic beds 20,000 feet above the sea; but 

 however it was managed, enough light material seems to have been 

 introduced beneath to float the mountains at about the proper height. 



We may conclude that, broadly speaking, the dry-land areas have 

 always been where they are now. The adjustments of the boundaries 

 of land and sea have been confined to the margins of the continental 

 masses. 



1 Jour. Gcol., vol. 22, pp. 131, etc. 



* Koninklijke Akad. v. Wetenschappen, Amsterdam, deel 24, pp 415-430. 



