The continental collisions crumpled the crust and pushed up huge
masses of rocks into several mountain belts throughout many parts of the
world (Fig. 116). Volcanic eruptions were extensive due to frequent conti-
nental collisions. During times of highly active continental movements, vol-
canic activity increases. This occurs especially at midocean spreading ridges
where new oceanic crust is created and at subduction zones where old
oceanic crust is destroyed. The amount of volcanism also affects the rate of
mountain building and the composition of the atmosphere, which greatly
influences the climate.
When Gondwana linked with Laurasia to form Pangaea, the collision
raised the Appalachian and Ouachita Mountains. Simultaneously, Laurasia
connected with Siberia, thrusting up the Ural Mountains. The continued
clashing of island arcs with North America resulted in an episode of moun-
tain building in Nevada called the Sonoma orogeny, which coincided with the
assembly of Pangaea 250 million years ago.
North America sat astride the equator, which ran from northern Mex-
ico to eastern Canada, during the Carboniferous 300 million years ago. It is
believed to have had a wet, tropical climate. A great river system, rivaling
today’s Amazon, ran down from the ancient Appalachian Mountains. It flowed
through valleys 20 miles wide while draining much of the continent. One
river system, which drained an area comparable to that of the modern Missis-
sippi River, had its headwaters in Canada’s Maritime Provinces. It flowed
southward for 2,300 miles, finally emptying near the present-day coastal plain
ofAlabama and Mississippi. A second river system began in south-central
Figure 116Major
mountain ranges resulting
from continental collisions.CARBONIFEROUS AMPHIBIANS