344 ROLLIN T. CHAM BERLIN 



active stages at about the same time, so far as correlations now 

 permit one to judge. It appears also from this study, that the 

 current divisions into periods which represent the general judgment 

 of geologists as to what are natural divisions, and which are based 

 on various considerations largely stratigraphic and paleontologic, 

 are in fair accord with the divisions that would be made if dias- 

 trophism were chosen as the primary basis of division. Such gen- 

 eral accord was to have been expected if diastrophism is a true and 

 fundamental basis for such division, but some divergencies in detail 

 were also naturally to be anticipated. 



The chief divergencies that have been found are the debatable 

 division line between the Cambrian and the Ordovician, and the 

 partially accepted separation of the old Carboniferous group into 

 Mississippian, and Pennsylvanian. It is notable that these division 

 lines are those that have been regarded as the least satisfactorily 

 established. Since the famous controversy of Murchison and 

 Sedgwick the Cambro-Ordovician dividing line has been a subject 

 of debate, and of uncertainty and oscillation of judgment. The 

 breaking-up of the old Carboniferous period and the recognition 

 of the lower portion as a distinct period under the name Missis- 

 sippian is a matter of recent date and is only partially accepted. 

 There is evidence of distinct diastrophism at the close of the Mis- 

 sissippian, but from present data it does not seem to be of the same 

 order of magnitude and prevalence as the deformations that mark 

 off the other periods, with the exception of the mooted Cambro- 

 Ordovician diastrophism. 



The Westphalo-Carbonide movement is brought by diastrophic 

 studies into more prominence than was given it under the criteria 

 that have been in common use.^ It appears to have been unusually 

 widespread and pronounced. On account of its magnitude, 

 dynamically and geographically, it seems entitled, under the dias- 

 trophic view, to be made to mark the beginning of the closing 

 scenes of the Paleozoic era. Shortly following it, and perhaps in 



' De Lapparent, however, states that while formerly it was thought proper to put 

 the coal beds all in one undivided period, one is now forced to observe that the coal 

 formations are traversed, between the Westphalian and the Stephanian, by an orogenic 

 phenomenon of such importance that it should be of greater weight than aU else in 

 determining the limit of the systems {Traite de geologie, 5th ed., II [1906], pp. 889-90)- 



