326 DAVID WHITE 
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 insufficient, 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 pennsylvanicum, 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 tchthatcheffianus, 
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- 
