48 ECONOMIC GEOLOGY OF SILVERTON QUADRANGLE, [bull. 182. 
makes all the important lodes radiate from one or more points — 
extinct volcanoes being generally preferred. That there is a certain 
radial disposition of the fissures will be presently shown, but this 
arrangement is very different from that which has been sometimes 
supposed, and which has been described in intendedly serious publi- 
cations. 
Having considered the various directions taken by the fissures in 
the region as a whole, it remains to discuss certain mutual relations 
in regard to direction exhibited by the fissures of several small areas. 
In spite of the wide diversity of strike already dwelt upon, and illus- 
trated in fig. 1, it is nevertheless true that in certain limited portions 
of the quadrangular area one or more systems of fissures, character- 
ized by fairly accordant directions of strike, are easily recognizable. 
In many cases these parallel fissures are so small and carry so little 
ore or vein matter that they have not been indicated on the map. 
Moreover, they are at places so closely spaced as to render it impos- 
sible to show them on the scale here employed for the topographic 
mapping. 
On the west side of Silver Lake Basin, in addition to the productive 
lodes, such as the Iowa, New York City, and Stelzner, the country 
rock is traversed by a great number of smaller fissures, striking from 
20° to 40° west of north, and resulting in a pronounced sheeting of 
the rock, generally parallel with the lodes mentioned, but without 
recognizable regular or rhythmical spacing. These fissures are nearer 
vertical, but one group of them sometimes exhibits a steep north- 
easterly dip, while another group dips southwesterly. Many of them 
are ore bearing, and it is not uncommon to see on a clean surface of 
rock a vein an inch or so wide composed of quartz and galena in 
about equal proportions. Such mineralized stringers may be seen to 
branch or to wedge out completely in a distance of 40 or 50 feet and 
be succeeded by an overlapping veinlet a few inches to one side. On 
a smaller scale they repeat the phenomena observed underground in 
the nearly parallel lodes, such as the New York City, belonging to 
Group II of the Silver Lake Basin lodes. (See detailed descriptions, 
pp. 145-148.) They appear to belong to the same system and to have 
been formed at the same time as the latter. 
Two prominent sytems of parallel fissures, intersecting nearly at 
right angles, are noticeable in the cliffs at the head of Arrastra 
Gulch. One system, with a strike of about N. 32° AY., and a dip of 
from 75° to 80° to the northeast, runs generally parallel with the 
trend of the gulch, and divides the compacted breccias of the Silver- 
ton series into great plates from a few inches to several feet in thick- 
ness. The width of this sheeted zone is from 30 to 40 feet. These 
fissures may perhaps be placed in the same system as those just 
described west of Silver Lake, and were possibly formed at about the 
same time. But they apparently contain neither ore nor quartz, and 
