336 E. O. ULRICH REVISION OF THE PALEOZOIC SYSTEMS 



Similarly the larger regions, whose general tendency is positive — anti- 

 clinoria, like Appalachia, Laurentia, and, to use a smaller example, 

 Ozarkia— these all include subordinate areas of negative tendencies. When 

 such regions are submerged it is these subordinate depressions that receive 

 deposits first and which retain them longest. Whether subsequently the 

 warps were merely accentuated, as in the case of Laurentia and Ozarkia, 

 or strongly folded, as in Appalachia, I question if the sedimentary evi- 

 dence of such submergences has in any case been entirely removed from 

 the structural depressions. However, as between gently warped and 

 folded areas, entire removal would seem to be much more likely in the 

 former than in the latter. 



Bearing on paleogeography. — The foregoing considerations have an 

 important bearing on paleogeography. The recognition of certain areas 

 as having positive tendencies and the discrimination of others as being 

 negative, and therefore more likely to be submerged than the former, 

 eliminates much of the initial uncertainty. Except, possibly,- in strongly 

 folded regions, where complications arise through faulting and unequal 

 resistance of formations to compression and erosion, the structural de- 

 pressions of today inherited their general features from similar depres- 

 sions of preceding ages, and this rule pertains to the small synclines as 

 well as to the great oceanic basins. But the attitude of synclinal areas 

 with respect to sealevel varied from time to time and is altogether rela- 

 tive. If the surface of a continent had been repeatedly and uniformly 

 warped so as to bring it partly beneath sealevel, the geographic features 

 at such times would have been much the same in each, and the resulting 

 expressions would be highly suggestive of a relatively stable earth and 

 the operation of simple sea filling and of other eustatic processes. But 

 the movements, while approximately uniform in tlie matter of kind nnd 

 nreas affected, were not so in amount of displacement, either as rcgai-ds 

 locality or time of occurrence. Comparing the frequently changing geo- 

 graphic patterns, it does not seem possible that the displacement of the 

 strandline is due solely to a raising of the sealevel, whether by sea filling, 

 land attraction, or equatorial bulging. On the contrary, the evidence 

 brought out by a close study of the distribution of marine sediments 

 shows conclusively that the strandline moved in obedience to locally vary- 

 ing oscillations of the surface of the lithosphere, and that submergences 

 and emergences are due to body deformations of the earth rather than to 

 any other known cause. 



Sometimes an area that under conditions of general subsidence was 

 commonly submerged remained above sealevel, while other relatively de- 



