No. 381.) A HALF-CENTURY OF EVOLUTION. 649 
climatic zones, from tropical lowlands with their vast swamps, 
to temperate uplands, stretching up perhaps to Alpine summits, 
with possibly glaciers of limited extent filling the upper parts 
of the mountain valleys. New Zealand at the present day has 
a subtropical belt of tree ferns, while the mountains ‘bear 
glaciers on their summits; and in Mexico, only about 20° from 
the tropics, rising above the tropical belt, is the temperate 
plateau, and farther up the subalpine snow-clad summits of 
Popocatepetl, Orizaba, and other lofty peaks. So in the Appa- 
lachians of the Paleozoic, the cryptogamous forests and their 
animal life may have been confined to the coastal plains and 
lowlands, while on the higher, cooler levels may have existed 
a different assemblage of life; and it is not beyond the reach 
of possibility that a scanty subalpine flora peopled the cooler 
summits. 
But the unceasing process of atmospheric erosion and river 
action continued through the Jurassic, which was, as stated by 
Scott in his /utroduction to Geology, “a time of great denu- 
dation, when the high ranges of the Appalachian Mountains 
were much wasted away, and the newly upheaved, tilted, and 
faulted beds of the Trias were deeply eroded.” At about the 
time of the opening of the Cretaceous the range was reduced 
to a peneplain (the Cretaceous peneplain), with only vestiges 
of once lofty mountains, the scenic features roughly recalling 
those of North Carolina and New England at present, although 
more subdued and featureless, more like the Kittatinny pene- 
plain of the Piedmont district at the eastern base of the Blue 
Ridge to-day as contrasted with the present mountain region 
of Pennsylvania and New Jersey. There were also extensive 
changes in the interior. What was the Colorado island was 
added to the mainland, and a great Mediterranean sea extended 
from the Uinta Mountains of southeastern Wyoming to New 
Mexico and Arizona, and stretched from the Colorado penin- 
sula westward to Utah. In the Upper Jurassic as the result of 
a depression a gulf was formed over northern Utah, Wyoming, 
and southern Montana (Scott). 
The formation of this Cretaceous peneplain was succeeded 
by a reélevation, and the surface which is now Virginia was 
