UPPER PALEOZOIC FLORAS 145 



attain the gigantic proportions nor the specific differentiation of their 

 Carboniferous successors; yet the relative homogeneity and the 

 great radial distribution of this flora argue for the absence of distinct 

 climatic zones in the recent sense while the apparent lack of annual 

 rings, so far as the woods have been specially examined, is opposed 

 to the idea of seasonal changes. 



Upper Mississippian. Probable greater severity of climate. — Our 

 knowledge of the flora of the uppermost part of the Mississippian is 

 too insufificient, both as to its composition and its geographical 

 distribution, to permit any very definite conclusions as to its province 

 and climatic environment. Some at least of the plants exhibit a 

 limited foliar expansion and semi-coriaceous character suggestive 

 of conditions far less favorable for growth than in the Pennsylvanian 

 ("Upper Carboniferous"), or even in the early Mississippian. They 

 seem to forewarn us of the great floral change which was, perhaps, 

 already in progress. From this highest stage may have come Dadoxy- 

 lon pennsylvaniaim, the only wood from the American Carboniferous 

 which appears on authoritative testimony to show annual rings, but 

 whose geologic age is unfortunately recorded merely as "Carbonif- 

 erous." Also it is possible that the Araucarites tchihatchejianus, 

 from western Siberia, said to have been found in the Carboniferous 

 limestone series, may belong to the same horizon. The occurrence 

 of severer climatic conditions with seasonal changes within upper 

 Mississippian time is provisionally admissible; but it is probable 

 that a radical climatic change attended the post-Mississippian eleva- 

 tion, the maximum variation being presumably marked by the climax 

 of the uplift. The paleobotanical revival which set in at the beginning 

 of the Pennsylvanian is known to all. Even in regions of supposed 

 continuous Mississippian-Pennsylvanian deposition the contrast 

 between the older and the younger floras (which do not really come 

 in contact) is very strongly marked. 



PENNSYLVANIAN (" UPPER CARBONIFEROUS") 



The Westphalian 



Environmental changes. — Following the retirement of the sea from 

 great areas at the close of the Mississippian (" Lower Carboniferous ") , 

 the new land surfaces were warped into new forms, with the produc- 



