InHuence of Country Rock. — Weed. 175 
The copper-veins at Virgilina, Va., which occur in meta- 
morphic schists formed from old igneous rocks, show a struc- 
tural feature common in the veins of the Southern States where 
the fissure crosses the rocks at less than ninety degrees to the 
schistosity. In such cases the veins show many spurs running 
off for short distances from the vein along the planes of the 
schist. The Blue Wing mine, at the locality mentioned, shows 
a diabase dike cutting the schists ; and where the vein crosses 
this rock it is narrowed and becomes a mere zone of plated 
rock. The spurs seen in some veins in granite are evidently 
the result of cross-fissures or joints, and not to be considered 
as a function of the rock itself. 
Where the veins pass from schists into quartzyte, as may 
be seen at Neihart, there is a marked change in their char- 
acter. This is well seen at the Big Seven mine, where a well- 
defined vein changes to many small fissures with shattered rock 
between. At Frenchtown, a small settlement east of Deer 
Lodge, Montana, the veins in andesyte-porphyry are strong 
and well-defined fissures, but do not cut any rock ; hence direct 
comparison cannot be made. At the Porphyry Dike mine, 
south of Rimini, Montana, the veins are small and tight in the 
granite, and open out in the rhyolyte into wide fissures, ill- 
defined, and really more like bands of shattered rock. 
This variation of fissures in different rocks is especially 
well shown at Cripple Creek, Colo., as described by Penrose,* 
and alluded to by Van Hise."!" In hard rock the fissures are 
sharp and clean-cut breaks, but in the soft rock they are ordi- 
narily mere series of very small cracks, constituting what Van 
Hise calls ''Distributive" faults. 
In slates the vein is commonly well-defined, as at Copper- 
opolis in ^lontana, and Parral, Mexico. In the Coeur d'Alene 
in Idaho, the veins cross slates and quartzites, and present only 
those minor peculiarities which might be expected in passing 
through such rocks — in fact, there is less change than one 
would naturally look for. 
Throughout the Appalachians the veins show a clustering 
of quartz-lenses whose ends overlap. These have been called 
"linked veins" by Becker, and "compression-veins" by Stretch. 
•"Mining Geologv of Cripple Creek District," by R. A. J. Pknrosk, Jr., 
16th Ann. Kept. U. S. Geol. Surv., 1894-5, part i, p. 144. 
t "Some Principles," etc., Trans., xxx., 35. 
