ISOSTATIC THEORY 
105 
at present, ample opportunity is given for crustal adjustment that 
finds final expression in the great earth plaits and cordilleral 
ranges of today. 
Then, also, the overthrust is generally little regarded. It is 
directly associated with the major flexing. No doubt it is a 
phenomenon that is much more widely efifective than is commonly 
suspected. With reference to the compressive fault dislocative 
fissure-veins appear as subordinate expressions of the same telluric 
stresses. If their prevailing strike chances to be subparallel to 
the line of overthrust relief from strain rather than normal to it, 
as might be expected, it may be merely another necessary con¬ 
sequence of the checkered character of the rock-masses. 
Although it might be inferred at first thought that fissure-veins 
originating under crusted stress should, in western America for 
example, trend north and south parallel to the strike of the thrust- 
rupture and also parallel to the desert range axis the fact that they 
do not does not necessarily indicate that their* genesis is of minor 
instead of major nature, or that it is orogenic rather than telluric 
in its fundamental character. 
Seemingly the secondary aspect is more apparent than real. It 
actually varies continually in different mountain ranges and even 
in the same range. This deviation appears to be partly depend¬ 
able upon tortional stress according to the abruptness, or ampli¬ 
tude, of individual orogenic structure. The latter, of course, is 
entirely independent of present mountain relief, which seems to be 
mainly erosional in character, if latest geological advises are to 
be accepted. 
The fact that in the majority of the desert ranges so many of 
the fissure-veins seem to strike nearly east and west may be due 
chiefly to the illusory circumstance that because of their ore-values 
these rupture lines are the only ones which are usually closely 
observed. In reality the primary jointing system of such mountain 
blocks is often decidedly radially disposed, the straight side of the 
semi-circle coinciding with the line where the steep face of the 
range cuts the plains surface. Any local set of fissure-veins is, 
therefore, only a limited and noticeable segment of a larger and 
more comprehensive scheme. 
Besides the steep dips which are so characteristic of so many 
fissure-veins and the latter’s prevailingly easterly strike, there is 
a third notable feature which must be closely linked up with them. 
