

STRUCTURE AND SURFACE FEATURES 401 
sufficient space of time, a similar fate must overtake all 
mountains. But a multitude of facts conspire to assure us 
that this level has no permanency. We know that certain 
mountain chains, after experiencing enormous denudation, 
have been submerged or partially submerged, and become 
eventually buried in whole or in part under fresh accumula- 
meme Of sediment, often of great thickness. Thereafter, 
crustal movements have again supervened; the old mountain- 
land has bulged up under the squeeze, and a new series of 
folds has been formed outside of and flanking the older 
series. With the re-elevation of the mountain area a new 
cycle of erosion is inaugurated, and in time the whole region 
may again be levelled, submerged, and eventually once more 
uplifted. Ranges which are the result of one earth-movement 
alone are termed monogenetic; those which, like the European 
Alps, owe their origin to two or more such movements are 
known as polygenetic chains. 
The younger folded mountains of the globe are typically represented 
in the Old World by the great east and west ranges of the Alps, the 
Himalayas, etc., and in the New World by the vast Cordilleras of South 
America and the Rocky Mountains of North America. These chains 
usually consist of a series of more or less parallel ranges, which often 
interosculate or merge into one another. Sometimes they extend con- 
tinuously in approximately straight or gently curved lines ; in other cases, 
a chain may be more or less strongly bow-shaped. Followed in the 
direction of the general axis, the mountains usually become progressively 
higher until, towards the central portion, the greatest elevations are 
attained, after which the heights, as a rule, gradually diminish in import- 
ance. While many mountain chains form a compact system of ranges 
throughout their whole extent, others divide and break up, as it were, 
into a series of divergent ranges. In all cases the width of a chain of 
folded mountains is greatly exceeded by its length. 
All these features, so characteristic of our younger chains, appear 
likewise to have distinguished the older folded mountains of the globe, 
many of which are now sorely wasted and reduced in height, while others 
have been wholly levelled. 
2. Dislocation Mountains —These are so termed because 
they owe their origin, not so much to folding as to fracturing 
and displacement of the crust. They usually occur in the 
form of more or less isolated heights or irregular shaped 
masses of elevated ground rising abruptly above adjacent 
lowlands. Mountains of this type are termed “ Horste” by 
German geologists, who cite the Harz Mountains as a 
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