318 ELEMENTARY GEOLOGY 
growth since the beginning of geological history; and disturb- 
ances of mountain folding have also frequently moved the rocks 
of the Far West, while in the Mississippi basin, between these 
regions, mountain folding has been nearly absent. 
Where mountains were first uplifted in early ages, others have 
been formed at later times, whenever the proper conditions have 
come to pass; and on the other hand, where there was no folding 
in early times, there has been less chance of later mountain devel- 
opment. Continents seem also to have been places of general 
and frequent uplift, while ocean basins have been regions where, 
on the average, subsidence has been in progress. In other words, 
ocean basins have been permanently basins, and continents have 
been permanently places of greater uplift. 
This theory of the permanence of mountains, ocean basins, and 
continents, does not mean that there are no exceptions, but that 
it appears to be a general law. Nor does it mean that a single 
mountain system has always been the site of elevation. While 
some mountains have been raised, and then worn down to their 
very roots without having suffered a second elevation, in some 
cases the same mountain chain has been uplifted more than once, 
or where this has not happened, other mountain chains have 
developed nearly parallel to them. 
Slowness of Mountain Growth. — The forces that 
cause the elevation of mountains, apparently do not 
produce sudden or even rapid elevation. Mountains are 
now growing in various parts of the world, and their 
growth is no less rapid than the average mountain 
uplift. While, at certain periods, and in certain places, 
mountains may have been uplifted more rapidly than 
any that are now rising, such swift action does not 
seem to have been the rule in the past. 
