496 C. SCHUCHERT CHRONOLOGY ON BASIS OF PALEOGEOGRAPHY 























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one another by disturbances that, as- 



made in most or all of the conti- 

 nents. The only established pe- 

 riods that in North America are 

 not yet known to have been closed 

 by marked crnstal unrest are the 

 Cambrian, Pennsylvanian, and 

 Paleogene. If, however, the newer 

 geologic chronology, which recog- 

 nizes eighteen post-Proterozoic pe- 

 riods, is to prevail, then there are 

 five additional times when North 

 America is not yet known to have 

 made mountains (Acadian, Croix- 

 ian, Ozarkian, Champlainian, and 

 Waverlian). I have no doubt that 

 these additional disturbances will 

 be found, but it is not essential to 

 the newer classification that the 

 deformation should have occurred 

 in North America. 



It is also now fairly well estab- 

 lished that the hydrosphere has 

 moved over the North American 

 continent at least twelve times and 

 in extent up to one-half of its area 

 (4,000,000 square miles). There 

 are, however, thirteen established 

 periods, and the only Euro- Asiatic- 

 flood failing of record in our conti- 

 nent is that of Permian time (see 

 figure 2). On the other hand, the 

 new geologic chronology recognizes 

 five additional times of flooding, 

 and only one of these is as yet 

 known to be closed by a disturb- 

 ance (Lower Cambrian or Wauco- 

 bian). In most cases, therefore, 

 the periods of either the old or the 

 new chronology are separated from 

 a rule, are marked by conformable 



contacts. It is because of this want of marked unconformity between the 



