GREAT BASIN OVERTHRUSTS 
259 
least confined to Mid or Late Tertic times. The same activities 
may be still going on at the present day. This is the same date 
that is commonly considered for the Basin Ranges generally. 
Such being the case crustal compressive and gravity faulting can 
hardly go on at the same time. 
As an actual, visible and diagrammatic representation of oro- 
genic example the Muddy Mountains disclosure is the most note¬ 
worthy and illuminating cross-section ever yet observed through¬ 
out the length and breadth of the Great Basin. It is the first and 
only exposure wherein an inferred fault-plane bounding a moun¬ 
tain block has been actually seen. The fact that this fault does 
not turn out to be a normal one, as hypothesis demands, or does 
not support the cherished Gilbertian contention of Basin Range 
origin matters little. Fault is, in truth, there. It is no fancy. 
It is as plainly displayed as a black-board diagram. No chalk 
artist could limn sketch more impressively than the phenomenon 
itself reveals unbrokenly for miles and miles along the mountain 
front. 
The entire face of the mountain is swept clean of all its waste 
and soil. The rock surfaces are as bare and as fresh as those of 
cabinet specimens. The relations of the different rock layers, 
through a vertical space of half a mile, are as succinctly portrayed 
as types on printed page. No rock section in all the world is 
painted in brighter hues or in prospect more contrasting. Through¬ 
out the desert the girdled mountain block, where no fault is dem¬ 
onstrated to exist, presents innumerable examples; Muddy Moun¬ 
tains alone actually reveal the phenomenon in all its pristine 
glory. 
In quality of lucidity the fault contrast between the Muddy 
Mountains of southeastern Nevada, and the Humboldt Range in 
the northwestern part of the same State, is as wide as the poles 
of Earth. Notwithstanding the fact that Louderback, one of the 
most ardent advocates of the Gilbertian hypothesis, so elaborately 
describes the Humboldt geology ^ in proof of the theory, his data 
really have no critical bearing upon the central theme. Moreover, 
a fault-plane having a 40-degree hade is strongest physical evi¬ 
dence that it is possible to adduce against both the urged hypoth¬ 
esis of Basin Range structure and the Duttonian theory of isos- 
tasy which it is intended to confirm. 
4 Bull. Geol. Soc. America, Vol. XV, pp. 289-346, 1904. 
