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THE APPALACHIAN OROGENY
Perhaps the most impressive landforms on Earth are mountain ranges, created
by the forces of uplift and erosion. Paleozoic continental collisions crumpled
the crust, pushing up huge masses of rocks into several mountain chains
throughout many parts of the world. Mountains have complex internal struc-
tures formed by folding, faulting, volcanic activity, metamorphism, and
igneous intrusion (Fig. 124).
The Appalachian Mountains, extending some 2,000 miles from central
Alabama to Newfoundland, were upraised during continental collisions
between North America, Eurasia, and Africa.This occurred in the late Paleo-
zoic from about 350 million to 250 million years ago during the construction
of Pangaea. The southern Appalachians were underlain with more than 10
miles of flat-lying sedimentary and metamorphic rocks, whereas the surface
rocks were highly deformed by the collision.
This type of formation suggests that these mountains were the product
of thrust faulting, involving crustal material carried horizontally for great dis-
tances.The sedimentary strata rode westward on top of Precambrian meta-
morphic rocks and folded over, buckling the crust into a series of ridges and
Figure 124Bear Butte
near Sturgis, South
Dakota,is an exposed
granitic intrusion called a
laccolith, showing outcrops
of upturned sedimentary
rocks around its base.
(Photo by N. H. Darton,
courtesy USGS)167PERMIAN REPTILES