Historical Geology Understanding Our Planet\'s Past

valleys (Fig. 125).The existence of sedimentary layers beneath the core of the

Appalachians suggests that thrusting involving basement rocks is responsible

for the formation of mountain belts,possibly since the process of plate tec-

tonics began. The shoving and stacking of thrust sheets during continental

collisions might also have been a major mechanism in the continued growth

of the continents.

The Mauritanide Mountain Range in Western Africa is the counterpart

(the other side) of the Appalachians. It is characterized by a series of belts run-

ning east to west that are similar in many respects to the Appalachian belts.

The eastern parts of the range comprise sedimentary strata partially covered

with metamorphic rocks that have overridden the sediments from the west

along thrust faults. Older metamorpohic rocks resembling those of the south-

ern Appalachians lie westward of this region, while a coastal plain of younger

horizontal rocks covers the rest. Furthermore, a period of metamorphism and

thrusting similar to the formation of the Appalachians occurred before the

opening of the Atlantic. In this respect, the two mountain ranges are practi-

cally mirror images of each other.

This episode of mountain building also uplifted the Hercynian Moun-

tains in Europe, which extended from England to Ireland and continued

through France and Germany.The folding and faulting were accompanied by

large-scale igneous activity in England and on the European continent.The

Ural Mountains were similarly formed by a collision between the Siberian

and Russian shields. The Transantarctic Range, comprising great belts of

Figure 125The Blue
Ridge Mountains in the
Appalachians, Avery
County, North Carolina.
(Photo by D. A. Brobst,
courtesy USGS)

Historical Geology