224 
ECONOMIC GEOLOGY OF SILVERTON QUADRANGLE, [bull. 183 
with the diamond drill. In general the longer axes of the ellipsoids 
appeal- to have been nearly parallel with the trend of the ore break. 
Individually, however, the ore bodies show much variation. Thus, on 
Ihc thirteenth level a streak of ore is recorded as bearing N. 30° W. 
They were commonly found by drifting along the "soft ground, " 
presumably fracture planes associated with attrition material and 
kaolin. A plan of the underground workings of the Guston mine 
(PL XV) shows a highly intricate and irregular maze of drifts and 
crosscuts running out in all directions from the shaft. The map, 
N°8d 
N?9d 
400 fk 
Fig. lti.— Longitudinal and transverse sections through the Guston mine. 
however, shows distinct evidence of a general elongation of the ore bod- 
ies, or of the ore-bearing ground, along an axis bearing about N. 20° E. 
As shown b}' the longitudinal section of the mine, the stopes attained 
their greatest aggregate length, about 600 feet, on the fifth level, and 
grew shorter below. Longitudinal and transverse sections of the 
"main ore body," compiled from a mine map made in 1890 and from 
the annual reports of the company, are shown in fig. 1G. The trans- 
verse section was evidently intended to show the general position of 
the so-called ore break, and not of the actual ore bodies. 
