PERMO-CARBONIFEROUS CLIMATIC CHANGES 633 
SURVIVAL OF NORTHERN, ‘‘COSMOPOLITAN,”’ TYPES 
The survival, in the northern province, of the Cosmopolitan, 
Carboniferous flora, which had been exterminated from the greater 
part, at least, of the GANGAMOPTERIS province, and its metamor- 
phism to the Cosmopolitan Permian flora, was presumably due to 
the generally low base-leveled state of the northern lands and the 
growth of the plants near tide level in regions bordering great bodies 
of water. ‘The greater retention of the sun’s heat by the sea and the 
greater humidity would co-operate with the low altitudes to neutralize 
the effects of atmospheric carbonic acid reduction. The contrast 
with the climate of the basins in the interior of the more elevated 
GaNnGAmopTeRis (Antarctic) continent could not fail to be great. It 
is worthy of note in this connection that in general the floral changes 
in passing to the Permian are least marked, the number of surviving 
later Carboniferous species being greatest, in those northern regions 
in which the post-Carboniferous uplift was least and there was less 
withdrawal of the sea. The best-marked illustration of this is fur- 
nished by the Appalachian trough in which the floral change is 
relatively gradual, the more characteristic Permian species being 
probably migrant from some more strongly affected region. The 
early moderation of the climate in Brazil so as to permit the return 
of a few hardy northern types and the enlargement of the GAN- 
GAMOPTERIS flora in other regions by the mingling of northern deriva- 
tives were presumably due to subsidence under loading of the basins; 
the general extension of the marine surface in the upper Permian; 
and, possibly, to a direct carbonic acid contribution attending the 
great vulcanism of the Permian. 
The flora of the Upper Permian is known in but few parts of the 
earth, but it is found that early in the Zechstein GANGAMOPTERIS 
and northern Permian elements mingled in the basins of northern 
Russia and the Altai; the northern Cycad, Pecopteroid, and Conif- 
erous elements had already invaded the GANGAMOPTERIS province, 
and from this mingling was developed a group which survived as the 
nucleus of a new world-wide Cosmopolitan flora, that of the Older 
Mesozoic. 
