bansome.] COORDINATION OF THE FISSURES. 45 
the fissures within and around this basin exceedingly numerous, bul 
many of them contain large and productive ore bodies. Another area 
is that of Galena Mountain, where the fissures are well exposed and 
form a remarkable network, but have not hitherto proved to contain 
ore bodies of great value. As still other centers of conspicuous As- 
suring may be cited the heads of Treasure and Poughkeepsie gulches, 
Ross Basin, and Mineral Point. These last four local districts of vig- 
orous fracturing are not distinctly separated, and should perhaps be 
included together as a single area over which Assuring and subse- 
quent veining has taken place on an extensive scale. Finally, the 
region embracing Savage, Emogene, and Silver basins, in the north- 
west corner of the quadrangle, in which are located the Virginius ami 
Smuggler-Union mines, may be regarded as part of a very important 
district of strong ore-bearing fissures, lying chiefly within the Tellu- 
ride quadrangle. 
COORDINATION OF THE FISSURES. 
By the coordination of Hie fissures is meanl their arrangement in 
natural systems, based upon direction, size, persistency, or other 
features. In the present instance the trends of the principal frac- 
tures will first be discussed, and afterwards the coordination of minor 
local groups of fissures occurring in various portions of the quad- 
rangle will be considered. 
If fissures were always vertical and were hounded by plane surfaces, 
it would be possible to represent them on a map, such as PI. Ill, by 
straight lines. Moreover, a single careful observation along a short 
exposure of any fissure would afford sufficient data for accurately 
laying off the direction of the line on the map. It might then be 
possible 1o classify these fissures with mathematical precision and 
divide them into groups or systems, each system being characterized 
by a certain common direction. 
But actual fissures seldom conform to these conditions. They 
stand at various angles to the horizon and are often curved. The 
existence of curves of large radii where it is evident that the mapped 
curvature is not the result of the combination of dip and topography 
is illustrated by several of the lodes plotted on the accompanying map, 
PI. III. The existence of minor curves maybe well seen in almost 
any plan of the underground workings of a mine exploiting a fissure 
deposit. These facts interfere materially with the discussion and 
classification of the fissures of a given region as a simple problem in 
plane geometry. It is obvious that single observations of the course 
of a fissure in a drift can not be assumed as giving its general strike. 
Nor is it practicable to tabulate such observations — at least in this 
region — and thereby to set up various systems of fractures traversing 
the region, each system narrowly confined and accurately distin- 
guished from other systems by a difference of only a few degrees in 
trend. 
