CHAPTER VII. 



INTERPRETATION OF THE ENVIRONMENTAL CONDITIONS 

 FROM THE EVIDENCE OF THE DEPOSITS. 



A. PERMO-CARBONIFEROUS CONDITIONS VERSUS PERMO- 

 CARBONIFEROUS TIME. 



From the preceding account of the stratigraphy of the upper Paleozoic 

 it is evident that a distinct line may be drawn between the red beds and the 

 beds beneath them in all of the provinces; it is equally clear that this line 

 will not lie at equivalent stratigraphic levels in all places. If, as is assumed 

 as the thesis of this paper, the red beds and their equivalents are indicative 

 of new environmental conditions, then a clear distinction may be drawn 

 between what has long been called Pennsylvanian and Permo-Carboniferous 

 (Permian) time, and Pennsylvanian and Permo-Carboniferous conditions, 

 and the two are not coincident in all places. 



The convenience and relative ease of synchronizing definite time inter- 

 vals with definite deposits for purposes of classification is obvious, but it is 

 equally obvious that time is not the sole nor even the dominant factor in 

 evolution. Environmental conditions are far more effective in determining 

 the rate and direction of evolutional and distributional changes, and these 

 conditions may migrate both vertically and horizontally, independent of 

 natural or arbitrary divisions of time. To assume that similar conditions 

 necessarily prevailed over large areas through even a minor interval of 

 geologic time is to introduce a possible error of the first dimension. This 

 warning is especially applicable in interpreting a series of terrestrial or semi- 

 terrestrial deposits. The evidence that changes in environment, climatic, 

 physiographic, topographic, and organic, migrate across large areas is too 

 full and conclusive to admit of any question that such processes are at work 

 at the present time. That such changes might have originated and migrated 

 in a strictly similar manner in past time is equally beyond question. When 

 past time is considered it is evident that migration may have proceeded in 

 a new direction, upward, for if the migration is a slow one the new conditions 

 will reach any new localities at progressively later dates and will be recorded 

 in stratigraphically higher deposits. 



The advance of conditions fitted for a certain group of organisms might 

 then be recorded in the stratigraphic series by observable changes which 



187 



