Davis — Bearing of Physiography upon Suess' Theories. 273 



spread opinion concerning the position of sea-level in epochs 

 anterior to ours" (ibid., i, 740 ; i, 782). For my own part, I 

 know of no complete disproof of the theory of subsidence, 

 enormous as its demands appear to be. It is in a certain sense 

 conceivable that the Bnral-bas-tau stood still, like a post in a 

 frozen pond, while all the rest of the world went down two 

 miles, like the sinking ice when the pond water is drawn off — 

 this being an analogy suggested by Suess himself (ibid., i, 736 ; 

 i, 774) ; nevertheless, in the absence of definite knowledge as 

 to the mechanics of the earth's interior, it seems legitimate to 

 entertain some more economical alternative hypothesis whereby 

 the Bnral-bas-tau and its fellows were locally uplifted about 

 two miles from their former lowly estate, as a result of rela- 

 tively local deep-seated movements of the earth's under mass, 

 about which the great body of the earth knew little. How 

 these deep-seated movements may be caused, it is impossible 

 now to say. Two methods of search may lead to the discovery 

 of their origin and character : one method proceeds partly 

 from general facts as to the density, temperature and composi- 

 tion of the earth, and partly from general speculations as to 

 cosmical history and the evolution of the earth ; the other pro- 

 ceeds from special facts as to the deformations that the earth's 

 surface has suffered, with abundant detail as to time and place. 

 In briefer phrase, one method seeks to determine the character 

 of the earth's internal movements from their causes ; the 

 other, from their effects. It will probably be long before 

 either or both methods reach a solution of so recondite a prob- 

 lem. In the meantime, it seems advisable to take the sea-level 

 as our standard of reference, and to speak of now high-stand- 

 ing isolated peneplains as locally uplifted, all the rest of the 

 world remaining relatively undisturbed, whether the forces 

 that produce the uplift are explained or not. 



Similarly, a graben may be spoken of as a sunken area, 

 when there is evidence that its position with respect to sea 

 level had been lowered, as would appear to have been the case 

 with the floor on which the Triassic beds of Massachusetts and 

 Connecticut were deposited ; but in such examples as the 

 Rhine graben it does not seem legitimate to measure the 

 amount of sinking from the level of the high-standing pene- 

 plains in the highlands on the east and west. 



In all these cases of local change the sea surface may be 

 provisionally regarded as fixed. A change in the level of the 

 sea must be universal, synchronous and of equal amount (except 

 for concomitant local changes in a land mass) along all shore 

 lines. A universal change should be accepted only when 

 demanded by widespread and accordant evidence, such as 

 Suess has in so masterful a manner brought forward in the 

 case of the world-wide Cretaceous transgression. 



