CHAPTER II. 



SUMMARY DESCRIPTION OF THE DIFFERENT PROVINCES OF 

 NORTH AMERICA IN LATE PALEOZOIC TIME. 



The primary attempt in this part of the work is to isolate as definitely as 

 may be a distinct interval of time and give such a description of the deposits 

 included in that interval that the life and the various factors of the environ- 

 ment, organic and inorganic, which have influenced the life may be studied. 



It is realized at the very outset that such an attempt is destined to only 

 partial success, for the nature of the geological record is in many places 

 such as to render the determination of the limits of the interval uncertain. 

 In places the interval began in a time of terrestrial deposition and ended 

 with the surface of the earth raised above the possibility of any accumulation 

 and with the geological record exposed to the obliterating forces of erosion and 

 the obscuration attendant on later earth-movements. In some other places 

 the limits are equally uncertain, because of other unfortunate conditions. 



Under the very uniform conditions of climate which, despite local abnor- 

 malities, prevailed over a large part of the earth's surface in the first part, at 

 least, of the interval, it is necessary to consider very wide areas as units, and 

 this introduces a new element of uncertainty, for while fairly accurate corre- 

 lations are possible over limited areas, broader correlations are difficult and 

 less certain, due to geographical interruptions in the exposure of the deposits. 



In the first intention the interval of time proposed for the study of life 

 was included in that which has been called by authors the Permian or Permo- 

 Carboniferous, but a very brief inspection of the stratigraphic data included 

 in the various papers and reports made it evident that no stratigraphic 

 limits could be assigned to this accepted interval which would coincide with 

 the climatological, biological, and erosional evidence. From this arose the 

 necessity of including in the consideration of the problem a considerable 

 thickness of strata both above and below the limits originally set and an 

 effort at correlation of conditions which were perhaps progressive in occur- 

 rence, rather than absolutely or approximately synchronous. 



In any case, or by the application of any methods, the continent of 

 North America shows three areas at the close of the Paleozoic within which 

 fairly close approximate correlations may be made by stratigraphic and 

 biologic evidence and between which correlations can only be made on 

 climatological and erosional evidence. These areas are: 



First, the upper Pennsylvanian and Permo-Carboniferous outcrops of 

 the eastern half of the United States and Canada, here called the Eastern 



Province. 



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