CLASSIFICATION^GRADATIONAL AND LITHOLOGIC CRITERIA 477 



is further manifested in the fact that this enormous thickness of early 

 Pottsville deposits occurs mostly in greatly deepened troughs that for long 

 preceding ages received no known deposits. This is true particularly of 

 the Ouachita troughs, in which the early Pennsylvanian Stanley shale 

 and Jackfork sandstone follow the Arkansas novaculite, a formation that 

 can not be younger than the Waverlyan and is most probably much 

 older — that is, Oriskanian. 



DEDUCTIONS BASED ON OB AD AT ION AL CRITERIA 



From the above incomplete array of facts and more or less probable in- 

 ferences, the following deductions may be drawn: (1) that the interior 

 regions of the continent from the Cambrian to the close of the Tennessean 

 never embraced areas high enough to favor rapid denudation ; ( 2 ) that the 

 clastic material in most of the Paleozoic deposits in southeastern North 

 America was chiefly derived from the relatively high lands bordering the 

 north Atlantic and the Gulf of Mexico; (3) that the Devonian dias- 

 trophic movements were not really more important than those in the 

 Ozarkian, Canadian, Waverlyan, and Tennessean periods; (4) that the 

 Devonian movements were inferior in consequence to the late pre-Cam- 

 brian, late Ordovician-early Silurian, late Tennessean-early Pennsyl- 

 vanian, and late Mesozoic-early Cenozoic deformations; (5) that the ])re- 

 domi nance of elastics in the Appalachian Devonian deposits, on which the 

 prevailing belief concerning the great importance of the movements of 

 this age is chiefly based, is due to the inland migration of belts of folding 

 (which at this time had reached areas contributing freely to the Ap- 

 palachian Valley troughs) and not to extraordinary activity, and (6) 

 that the late Tennessean-early Pennsylvanian period of deformation is 

 the third of four coordinate, grand periods of diastrophic activity. For 

 the sake of completeness, it may be said that the fourth of these grand 

 periods began in the late Cretaceous, the second in the late Ordovician, 

 and the first in the pre-Cambrian. 



LATERAL CHANGE IN CHARACTER OF SYNCHRONOUS DEPOSITS WITHIN THE 



SAME BASIN 



Change not the rule. — It is commonly believed that all synchronous 

 deposits change more or less decidedly when followed from place to place. 

 This conception being founded on familiar conditions prevailing along 

 the seashores of today, it naturally commands credence and res]iect. 

 Perhaps no other partial truth has done more to impede ])rogress in 

 stratigraphic correlation and paleogeography than this plausible fallacy. 



