UPPER PALEOZOIC FLORAS 335 
with the return of some of the northern types to portions of Gondwana 
land, and, secondly, with the fitness of some of the Gondwana types, 
especially Glossopteris, Phyllotheca, and Noeggerathiopsis, not only 
to join with Walchia and Callipteris in the Zechstein flora of northern 
Russia, but later to meet with Podozamites, Ctenophyllum, Cladophle- 
bis, Clathropteris, and Dictyophyllum, under the mild climatic con- 
ditions of the early Mesozoic. Glossopteris, perhaps most adaptable 
of the older Gondwana types, was able to reach as far as the supposed 
Rhetic of Tonquin where it is last seen. 
Glaciation.—It appears, therefore, that the interval, or better the 
intervals, of glaciation in Gondwana land were of relatively short 
duration as compared to all Permian time, though the thickness and 
distribution of the glacial deposits indicate a magnitude far exceeding 
that of Pleistocene glaciation. At the same time it seems improbable 
that refrigeration could have occurred in so many regions of the 
southern and eastern hemispheres, even approaching the equator, 
without some corresponding, though unequal, changes of world-wide 
extent. Concerning this very important point, the evidence is quite 
inconclusive and the opinions varied. 
American Permian types derived from Europe—Il{ we compare the 
plants of eastern America with those of western Europe we find the 
greater changes in Europe where the extensive orogenic movements 
and attendant shifting of basins of deposition doubtless stimulated 
the evolution of the Permian flora. On the other hand, in the Appa- 
lachian trough, where environment was but little affected by orogeny, 
and where sedimentation was uninterrupted, there is only gradual 
change, many of the Stephanian types persisting far up in the Dunkard 
formation. ‘The relatively few species characteristic of the Euro- 
pean Permian which occur in the Dunkard, and which were not able 
to conquer the older flora under the conditions then existing, are 
clearly migrants from western Europe. It must be noted, though, 
that both West Virginia and Kansas exhibit new generic types, the 
products of local conditions, that have not been found outside of these 
regions. On the other hand, Walchia, which is present in Kansas 
and New Mexico has not yet been discovered in the Appalachian 
trough though it is present in the Nova Scotian basin, which seems 
to have been in closer touch with Europe at this time. The floral 
