BAnsome.] COORDINATION OF THE FISSURES. 49 
may be of later dale. The .second set of fissures, with a strike of N. 
60° E., and a southeasterly dip of about 80°, crosses the gulch near 
its head, and may be seen also in Blair Gulch, in a considerably 
broader zone than the first set. Some of these fractures contain 
quartz, but, so far as observed, are not heavily mineralized and carry 
only a little pyrite. The relative ages of these two systems of inter- 
sect in»- fissures were no1 directly determinable in the field. It is not 
improbable thai they were formed simultaneously as conjugate fis- 
sures. (Soo pp. 52-53). 
Minor systems of fractures in parallel coordination may be well 
studied <»n Galena .Mountain, a precipitous peak composed of both 
massive and Fragmental andesite. The mass of the mountain is cut 
fcby very numerous fissures, many of them prominently indicated on 
the surface as lodes orveins. These may be divided into four groups, 
the members of each group being characterized by approximately the 
following strikes: ( 1 ) X. L5 E., (2) X. and S., (3) X. 25° W., and (4) 
X. 65° \Y. In each of these systems there usually occurs one or more 
fairly strong lodes accompanied by numerous smaller, nearly parallel, 
fissures, the rock being conspicuously sheeted. These associated par- 
tllel fissures are particularly abundant in theX. 25 W. system, asseen 
m the southern declivity of the mountain, in the vicinity of the Veta 
Madre mine. They are generally nearly vertical, and rather closely 
jpaced, a foot or less apart. They are usually occupied by small 
reins which sometimes carry ore minerals, chiefly galena, sphalerite, 
ind chalcopyrite, but which are seldom large enough or rich enough 
o be worked. 
Another area within which the fissures exhibit striking parallel 
;oordination is on Treasure Mountain and at the head of Placer Gulch. 
rhe dominant northeast-southwest fissure system of this portion of 
he quadrangle is exemplified by a series of strong, persistent lodes, 
epresented by the Sunnyside and Scotia, with a general course of 
/bout N. 40° E. The dip of these is southwesterly at high angles. A 
econd system of shorter, less conspicuous fractures crosses the first 
eries almost at right angles, with a general course of about N. 55° W. 
liese fissures are nearly vertical, but the majority of them dip south- 
west at high angles. In their trends these fractures belong with the 
ystem of northwest-southeast fissures already recognized as a system 
haracteristic of the quadrangle as a whole. It is interesting to note 
aat here, however, they are not, as in the Silver Lake Basin, the 
laster fissures, but are short, transverse, relative^ unimportant frac- 
ires, forming a nearly rectangular network with the strong, contin- 
ous northeast-southwest lodes. A third local system of transverse 
Bins, represented by the Golden Fleece, has a course of about N. 
5° E., with usually steep southerly dip. Still a fourth set of very 
fcminent lodes is exposed at the head of Placer Gulch, with an 
rerage strike of about N. 25° E. Their dips are usually steep and 
Bull. 182—01 -i 
