Febbuabt 12, 1909] 



SCIENCE 



259 



structui-e lines of Asia were largely estab- 

 lished. By the Cretaceous, however, Asia was 

 again, a low and featureless continent. 



The Cenozoic history is one of erosion and 

 land deposit. The Cretaceous peneplain con- 

 ditions were continued at least in southern 

 Asia through the Eocene and Oligocene and 

 well into the Miocene, when occurred the epoch 

 of mid-Tertiary compression resulting in fold- 

 ing. Since then there have been extreme 

 effects of vertical warping unaccompanied by 

 folding and chiefly of Pleistocene age. The 

 evidence of the latter is largely physiographic 

 and indicates " one of the most remarkable 

 diastrophic movements of which we have 

 knowledge." The Neocene and Pleistocene 

 warping and faulting are believed to have 

 produced differences of elevation exceeding 

 20,000 feet. Davis and Willis are thus in 

 accord and stand in opposition to the earlier 

 views of European geologists, in that these 

 American investigators hold that the eleva- 

 tions due to Permo-Mesozoic folding or older 

 epochs of diastrophism were long since planed 

 away by erosion and are not the causes of the 

 present relief. These views, developed first in 

 America, are thus made of circumterrestrial 

 application and may be regarded as the gTeat 

 contribution of physiography to geologic 

 theory. 



The paleogeographic maps are a feature of 

 this report, as is also the map showing the 

 results of the recent diastrophism. 



In the final chapter Willis considers the 

 bearing of the previous facts and conclusions 

 upon the problem of the continental structure 

 of Asia. No adequate outline of this chapter 

 can here be presented. In brief, however, he 

 finds that the continent may be resolved into 

 positive and negative elements, the former 

 areas tending to stand high, the latter tend- 

 ing to stand low. These tendencies are latent 

 during comparatively long periods of quiet 

 and resultant peneplanation, but become op- 

 erative during epochs of diastrophism. The 

 compressive movements, on the other hand, 

 have pressed and welded the positive elements 

 together, the axial directions of folding repre- 

 senting the compression of the negative zones 

 lying between. 



The cause of the diastrophism Willis as- 

 cribes to differences in specific gravity, re- 

 stricted according to Hayford's determination 

 to the outer hundred miles of the earth's body; 

 the vertical movements being chiefly due to 

 isostatic readjustment between the several 

 continental elements, the compressive move- 

 ments being due to the tendency of the heavier 

 oceanic segments of the earth to spread and 

 underthrust the outer portions of the whole 

 continental mass. 



For more than a third of a century the 

 incompetency of secular cooling of the outer 

 crust to account for diastrophism has been 

 pointed out,' though it still finds credit in 

 many text-books. Chamberlin, recognizing 

 this, has constructed a hypothesis by which 

 periodic compressive movements are ascribed 

 to a shrinkage of the centrosphere and not the 

 lithosphere. Willis goes still farther and ob- 

 viates the necessity of postulating shrinkage 

 of either the inner or outer earth. His hy- 

 pothesis thus belongs to that group to which 

 O. Fisher and Dutton have previously con- 

 tributed. 



This must be regarded as a most suggestive 

 working hypothesis, opening the field still 

 wider to investigation, and may serve to de- 

 stroy still more the false confidence regarding 

 the cause of erustal movements which was felt 

 by geologists of a previous generation, owing 

 to the narrowly limited hypotheses then in 

 vogue. 



The hypothesis advanced by WiUis is an 

 extension of that proposed by Dutton, who 

 ascribed folding to that subcrustal horizontal 

 creep from the low toward the high elements 

 which is necessary to isostatically restore the 

 initial elevation of the high and the initial 

 depression of the low.^ 



In the form in which Dutton stated the 

 hypothesis it appears insufficient, since the 



' C. E. Dutton, " A Criticism upon the Contrac- 

 tional Hypothesis," Amer. Jour. 8oi., Third Series, 

 Vol. VIII., pp. 113-123, 1874. 



^ C. E. Dutton, " On Some of the Greater Prob- 

 lems of Physical Geology," Bulletin of the Philo- 

 sophical Society of Washington, Vol. XI., pp. 51- 

 64, 1889. 



