190 



ENVIRONMENT OF VERTEBRATE LIFE, ETC. 



As noted above, the progress of Permo-Carboniferous conditions during 

 Pennsylvanian and Permo-Carboniferous time is marked by the disappear- 

 ance of marine and swamp conditions and the appearance of more purely 

 terrestrial deposits. The change from swamp to terrestrial deposition is 

 marked more by the chemical condition than the physical character of the 

 material — that is, the change was more in the climate than in mode of depo- 

 sition. 



As the climatic change was the most significant factor in the devel- 

 opment of the land vertebrate life, and as its progress is most strikingly 

 marked, it is taken as the key for the interpretation of the whole environ- 

 mental migration. 



As has been shown in the summary of the stratigraphy of the different 

 provinces, in the correlation tables i and 3, and in the accompanying schem- 



FiG. 5. — Diagram illustrating the record of a progressive wave of definite conditions advanc- 

 ing across an area in which continuous sedimentation is in progress. The upper and 

 lower limits of the sediments deposited during the continuance of the definite condition 

 will lie obliquely to the bedding planes. The upper and lower limits may be marked by un- 

 conformities or disconformities, but not necessarily. 



Fig. 6. — Diagram illustrating the record of a progressive extension of conditions which persist 

 at the point of origin. The lower edges of the deposit formed during the definite condi- 

 tions will be oblique to the bedding planes, but the upper edge may be straight, forming a 

 wedge of the particular sediments, or the upper edge may be above the plane of erosion. 

 Such a wedge will be formed only if sedimentation is continuous at the point of origin of the 

 progressive conditions. 



atic diagrams (figs. 5 and 6), the climatic change is recorded in conglomer- 

 ates, glacial deposits, and red beds and can be clearly traced from east to 

 west in a line ascending obliquely across the stratigraphic series from the 

 middle of the Conemaugh in the Eastern Province to the base of the so- 

 called Permian in the western provinces. The base of this series of red beds 

 and conglomerates marks the beginning in each region of Permo-Carbon- 

 iferous conditions, and the upper limit is lost by erosion or lack of deposi- 

 tion, or merges into the very similar Triassic deposits. 



Permo-Carboniferous conditions in the Eastern Province are not coinci- 

 dent with Permian strata of current classification, but occur in a part of the 

 Pennsylvanian strata as well; they encompass a definite period, however, 



