4fi ECONOMIC GEOLOGY OF SILVERTON QUADRANGLE, [bull. 182. 
In the Silverton region the important fissures have been mapped in 
the field with reference to the topography. The lines as shown are 
approximations to truth, requiring much allowance for necessarily 
limited observations and for imperfections of the topographic map. 1 
Inspection of the map on which the prominent lodes are thus platted 
shows that the most conspicuous Assuring has taken place in a general 
northeast and southwest direction. The dip of these fissures is usually 
southeast at about 75°. But the angles of dip range from 40° to ver- 
tical, and a few of the lodes dip northwest. Perhai^s slightly less 
marked, but thus far more economically important, are numerous 
strong lodes running in a general northwest and southeast direction. 
In the southeastern quadrant these usually dip northeast at angles 
varying from 50° to 90°. Elsewhere the} 7 usually, although not inva- 
riably, dip southwest at high angles, as observed by Purington in the 
Telluride area. The existence of these two dominant directions was 
long ago pointed out by Endlich. 2 Purington, 3 in his description of 
the fissures of the neighboring Telluride quadrangle, concludes that 
"there are four general directions of Assuring: (1) East and west, and 
(2) northeast, best developed in the central and southeastern portions 
of the quadrangle, and (3) north and south, and (4) northwesterly, 
best exemplified in the northwestern portion." It will be seen that 
the two most prominent directions of Assuring in the Silverton area 
coincide with Purington's second and fourth general directions in the 
Telluride quadrangle. 
There occur in the Silverton quadrangle several approximately 
north and south, as well as nearl} 7 east and west, lodes, and if atten- 
tion were restricted to certain small areas, such as Galena Mountain, 
it might be considered advisable to recognize one or both of these 
directions as characterizing distinct subordinate systems of fractures. 
Such a grouping, however, while valid for the very limited area named, 
is lost when the various directions of all the fissures in the quadrangle 
are taken into account. The possible number of such subordinate 
systems then becomes so large as to obliterate the divisions between 
them. For accounts of these minor directions of fracturing the reader 
is referred to the latter part of this section, where their coordination 
is discussed, anekto the detailed descriptions of the various local groups 
of lodes in the later pages of this report. It is sufficient in this place 
to point out that the Assuring of the rocks throughout the quadrangle 
has been so thorough and has taken place in so many directions that 
two of these only stand out as dominant. Even these show a cer- 
tain localization within the limits of the quadrangle, the northeast- 
southwest fissures notably predominating in the northeast quadrant, 
1 The topographic map upon which most of the lodes were originally laid down was partly 
revised during the year 1900, and these lodes had then to be transferred and adapted to the new 
map in the office — a procedure which may lead to occasional unavoidable errors of position 
with reference to minor topographic features. 
2 Hayden Survey, Ann. Kept. 1874, p. 232. :t 1 .< .<-. cit , p. 7t>7. 
