432 



E. O. ULRICH REVISION OP THE PALEOZOIC SYSTEMS 



pended intensity. The second cause, alternating with the first, is thought 

 to be the seaward pressure produced in the process of "continental creep" 

 suggested by Chamberlin and Salisbury. Both would result in accentua- 

 tion of the interior warps or domes, and in either process the greater 

 arching would occur on the far side. This side then would tend to eleva- 

 tion, while the near side, on the contrary, would be relatively depressed 

 and the more likely to be submerged on the next advance of the waters. 

 (See figure 14.) Loading may have been a contributory cause of the 

 more general elevations. (See following note on faulting.) 



That sedimentary loading did not cause the differential vertical move- 

 ments of the median areas of uplift that are referred to under the term 







j 



Ifl 





"^ 1 ^X. ^**'"->.«*^ SEA LEVti..^ 





^ -^^^ 



1 

 1 



1 """^ 





^l^-""^ — 



"*~"~^~^^r'*- ^ 1 SEA LEVEL 







1 



^""^^^L 







j ....._ 





1 

 1 

 1 

 1 





__d4— — — 



" ~~— -n^-.^ SEA LEVEL 









1 

 1 



\ 



Figure 14. — Diagram illustrating Tilting 



The diagram illustrates "tilting" of interior areas of uplift (for example, the Cincin- 

 nati dome), and the causes of the alternate overlap and retreat of the sea on their 

 opposite sides. Arrows indicate direction of pressure. The letters A, A', A", B, B' 

 and B" mark the same points in the three stages. 



"local oscillations" is proved by the fact that the side which received the 

 load in one stage is often the one which was emerged in the next. Ob- 

 viously, if loading had been the controlling factor in the local vertical 

 movement, then the submerged side would have continued to subside and 

 thus have acquired a further load in the next succeeding advance of the 

 waters. In fact, however, in the cases described, directly the opposite of 

 what should be expected under loading occurred repeatedly. Sedimentary 

 loading is thought to be a dominant factor among the immediate causes of 

 local or general subsidence only in the median parts of great synclinal 

 thoughs or depressions. It seems to have been but rarely, if ever, effect- 

 ive in the way of dragging down the immediate flanks of inland domes. 

 On the contrary, loading is more likely to induce accentuation of slope 

 with relative elevation of the near shore land than subsidence. 



Note respecting normal faulting. — Formal faulting constitutes one 

 of the most striking and convincing proofs of differential vertical dis- 



