18 Joseph LeConte—Genesis of Metalliferous Veins. 
_ movement, the rock along such a fractured and loosened plane 
may be broken into small fragments like rubble. Such a plane 
of shattered rock—such a fissure filled with rubble of country 
rock—by deposit forms a brecciated vein, i. e. a mere rubble 
of country rock cemented with vein matter often rich in metals. 
Examples of such veins are not uncommon. In the Bassick 
mines near Silver Cliff, Colorado, the vein consists of a rubble of 
trachytic rock cemented together with argentiferous galena. 
fine specimen of this remarkable vein stone, is now in the 
University Museum.* In the carbonate mines, San Francisco 
district, Heels Co., Utah, the vem which is 2 ‘feet thick, con- 
esitic breccia with a cement of alena.t In the 
Ca tcuse a mine at Sulphur Bank, Lake Co., California, the vein 
isarubble of shale and sandstone country rock, ceménted 
with silica and sulphides of iron and mercury, and the process 
is still going. 
Substitution veins.—Again: if the country rock be soluble, 
as for example limestone, then the country rock may be re- 
oved in the course of the subterranean waters, and similar or 
different and less soluble matters may be deposited in its place. 
These are substitution veins. In fact the stalactitic and sta- 
and also of Leadville§ come under this head. Probably also 
many so-called segregative veins may come under this head. 
They are irregular substitution veins. 
e. Contact veins.—It is obvious that immediately along a 
plane of contact between igneous and stratified rock, or between 
* The breccia of Bassick mines is somewhat similar - that . ‘egg ras ~~ 
It consists fragments of country rock slightly rounded at corners 
edges and covered with several layers of metallic sulphides. The evidence at 
deposit fro bay ascending wikers is comple’ ‘or an interesting account by 
Grabill, of er ingens mine, see Tra of Am. Institute of Mining 
Engineers for 
+ Bec stati leg f U. 8. Geol. ak p. 38. 
At Leadville the country rock i Ss ackeaaiels limestone with interealary beds 
of porphyritic trachyte. The sowie ei supposed to have been in the porphyry 
in a finely disseminated condition, and to have been leached out and accumulated 
in hollowed-out channels in the limestone, in a e of iron, manganese and 
clay, partly or wholly filling the cavities. The ore was originally i in the form of | 
waipiade. but some of it is changed into oxides and carbonates Emmons, Rep. of — 
U. 8. Geol. Surv. for 1881, pp. 203-231. ; 
