

402 STRUCTURAL AND FIELD GEOLOGY 
prominent example. They are usually composed of very old 
rocks, and are severed by vertical dislocations from the low 
tracts that surround them. If the student will imagine a 
broad and lofty plateau to be cracked across in different 
directions by profound fractures, and the dislocated plateau 
to settle down irregularly, he will have some notion of the 
origin of Horste. Those segments of such a fractured plateau 
which have retained their original position are Horste, and they 
therefore testify to a former higher crustal level (see p. 179). 
Occasionally, dislocation mountains occur as a series of 
parallel ranges, separated the one from the other by large 
vertical dislocations or normal faults. The ranges of the Great 
Basin, which extend north and south between the Sierra 
Nevada and the Wasatch Mountains, are of this type, and of 
similar origin are the Vosges and the Black Moresty ime 
VOSGES’ RHINE BLACK FOREST 
te ieee ie as re A rey: ‘ef - a 
¢ i, 
ty eae “i ok | ae 
FIG. 143.—SECTION ACROSS THE VOSGES AND THE BLACK FOREST (PENCK). 

1. Granite, etc. ; 2-7, Mesozoic rocks ; 8-9, Tertiary and later beds. 
escarpments of these two mountain ranges face each other, 
separated the one from the other by long parallel lines of 
faults, between which the broad depression of the Rhine came 
into existeneei{see Fig. 143), 
Dislocation mountains, like all other elevations, become 
modified by erosion and denudation, and are met with now 
in every stage of dissolution. Speaking generally, we may 
say that the best preserved examples are of relatively recent 
geological age. But some prominent Horste are of very 
great antiquity, their persistence being due to the simple fact 
that they consist of more durable rocks than the low-lying 
tracts above which they rise. In every case, however, it can 
be shown that such Horste have experienced excesSive 
denudation. 
3. Laccolith Mountains.—The leading characters of lacco- 
liths have been discussed in Chapter XIII. Mountains of this 

