56 ECONOMIC GEOLOGY OF SILVERTON QUADRANGLE, [bull. 182. 
opposed to the idea that any considerable tangential displacement of 
the walls had taken place during their opening. In the King lode, south 
of Silverton, and in other fissures cutting the schists, there is no recog- 
nizable displacement or throw of the individual schistose bands by the 
Assuring. Slickensiding of the fissure walls prior to the deposition of 
the ore has been nowhere recognized. In the Telluride quadrangle, 
where the occurrence of workable lodes in nearly horizontal sediments 
gives better opportunities than are usually available in the Silverton 
area for detecting and measuring displacement, Purington 1 evidently 
saw little clear evidence of it. Beyond recording a vertical separation 
of 1 foot by normal faulting in the San Bernardo mine, and conclud- 
ing from the shape of the ore bodies of the Virginius and Smuggler- 
Union mines that the spaces they occupy were probably formed by 
faulting of the same kind, he makes no further reference to faulting 
as accompanying the formation of the ore-bearing fissures, although 
pointing out the desirability of future study in this direction. In 
nearly horizontal rocks faulting in which the movement is confined 
chiefly to the horizontal component (offset or heave) is not readily 
detected when of small amount, and was noted only in the few cases in I 
which later-filled fissures have cut productive lodes, displacing the 
latter. 
The absence of considerable displacement as an accompaniment of 
the opening of lode fissures is not a special peculiarity of the Silverton 
quadrangle, but is of very common occurrence. In fact, it seems to 
be comparatively rare to find more than very moderate faulting in 
fissures which have formed productive lodes. 2 
INTERSECTIONS AND RELATIVE AGES OF FISSURES. 
In a region where the fractures are so numerous and possess such 
diverse trends intersections must necessarity be of frequent occur- 
rence. But as veins at such points are particularly susceptible to 
disturbance by later movements of the rocks and to superficial disin- 
tegration, the study of these intersections is often difficult. The pres- 
ence of seams of clay or gouge, due to these later or postmineral 
movements and the entrance of oxidizing waters, may so obscure the 
original relationship at the junction of two fissures as to render any 
conclusive determination of relative age impossible when no conspicu- 
ous faulting of one of the fissures has taken place to give the desired 
information. 
In many cases in the Silverton quadrangle intersecting fissures have 
been formed nearly or quite simultaneously and filled by one process 
of vein deposition. This is true of the assemblage of branching fis- 
sures worked in the Silver Lake and Iowa mines, and probably so of 
the Placer Gulch and Lake Como fissures. It is also possible that 
Loc. cit.,p. 780. 
Phillips and Louis: A Treatise on Ore Deposits. London. 1896. 
