396 E. O. ULRICH REVISION OP THE PALEOZOIC SYSTEMS 



shown that they are able to lower the continents approximately to the sea- 

 level in a fraction of geologic time. The continents would therefore have 

 long since disappeared, if they had not been rejuvenated by renewed rela- 

 tive elevation or the withdrawal of the sea. . . . There are some sub- 

 merged dependencies and intercontinental connections. ... In the 

 earlier eras, when the differentiation of platforms and basins was less ad- 

 vanced, ridges which have since been submerged are perhaps recognizable. 

 . . . In the earliest known ages, these may have been rather numerous 

 and their combined area considerable, but these seem to me to be only 

 qualifying features which, by the natural place in evolution which they 

 fill, support, rather than weaken, the general conception of a symtematic 

 succession of deformations in which the offspring of each is parent of the 

 next, and in which both continents and ocean basins were progressively 

 segregated and unified." 



The latter of these two conceptions is held rather generally by American 

 geologists. The results of my own investigations tend to show that it 

 holds true not only for the continents and oceanic basins on the whole 

 but also for relatively small portions of each continent. Once started, the 

 areas of relative uplift have always continued to be areas of stratigraphic 

 overlap or of land, while the relatively depressed areas remained as a rule 

 areas liable to subsequent submergence. Though the surface of the litho- 

 sphere was affected by innumerable minor differential vertical and hori- 

 zontal movements and the strandline is forever changing, the continents 

 and the oceanic basins yet permanently retained essentially similar geo- 

 graphic relations to each other. The truth of this conception, especially 

 in so far as it concerns continental areas of elevation and depression, is 

 abundantly attested by detailed studies of the formations in and around 

 areas of Eopaleozoic rocks. Some evidence of this kind may be gleaned 

 from the introductory chapters, and more from following pages describing 

 vertical movements of median continental areas and corresponding oscilla- 

 tions of continental seas, while considerable additional information re- 

 specting localities of repeated overlaps is in hand and ready for publica- 

 tion through other channels. 



Willis's views on permanence of oceanic basins. — Chamberlin (op. cit., 

 page 688) in saying that "there are some submerged dependencies and 

 intercontinental connections,'' takes a broad and liberal stand respecting 

 the probable former existence of considerable landmasses in areas now 

 covered by the great oceans. Willis,^* however, though he does not com- 



3* Bailey Willis : "Principles of Paleogeography." Science, vol. xxxi, No. 790, 1910, 

 pp. 243-246. 



