UPPER PALEOZOIC FLORAS 339 
distinct terrestrial climatic zones, possibly completely into the polar 
regions. 
Some of the criteria above mentioned are susceptible of different 
interpretations; but taken collectively they appear to admit of but 
one conclusion. Whether or not we admit that climatic changes may 
be caused by reasonable or practicable changes in the amount of 
carbonic-acid gas in the air it is certain that in geological times the 
vegetation of the earth must have been more or less influenced by the 
constitution of the atmosphere from which the plant derives so 
important a part of its real food. 
Gradual loss of uniformity of climate, with brie} glacial interruption 
in Permian.—As has already been indicated the Westphalian probably 
witnessed the greatest extension of uniformity and equability of 
climate over the earth. In the Stephanian the flora is hardly so 
homogeneous, though the world-climate appears still to have been so 
equable as to allow free migration of the larger part of the flora from 
a moderate latitude on one side of the equator to the opposite without 
encountering seriously obstructive seasonal changes. In the Permian 
the regional distinctions between the floras are much clearer; and 
presently climatic zones, and consequently botanical provinces, are 
recognized. Yet, about the North Atlantic the climate of the Lower 
Permian was still relatively uniform so that moderately free migration 
of the floras without the development, so far as we know, of pro- 
nounced annual rings, took place in the Autunian of France, the 
Permian of Prince Edward Island, the Dunkard of southwestern 
Pennsylvania, the Chase of Kansas, and the Wichita of Texas. 
Red beds and climate.—It will be remembered that the period now 
considered is characterized in western Europe, England, Eastern 
Canada, the Appalachian trough, and the Western Interior basin, by 
the deposition of red beds which in some areas carry deposits of 
gypsum, etc., and which are generally regarded as laid down under 
an arid climate. Viewing the matter from the paleobotanical stand- 
point, we may ask whether equability and uniformity of climate, such 
as is shown by the fossil floras, is compatible with aridity in latitudes 
so high as northern England and the Gulf of St. Lawrence. If all 
the regions of Permian red-bed deposition were arid it would seem 
that humidity could not have been essential to equability of climate. 
