ORE-FORMATIONS 253 

this way are liable to be filled with subsequently introduced 
mineral matter. It has frequently happened, therefore, that 
fissured rock-masses have been permeated by ore-bearing 
solutions to such an extent that the rock can be mined in 
successive floors, forming what is known as a Stockwork (see 
Fig. to1). The infinitely numerous veins, veinlets, strings 
Poi Lg ad 
oe bad i, 
= 
FIG. IOIL—STOCKWORK. 
gn, gneiss, etc. ; g, granite. 






and threads of ore branch and interlace often in a most 
confused and irregular manner, although sometimes they 
tend to traverse the rock in certain more or less definite 
directions. The richness of a stockwork is frequently 
increased by the impregnation of the rock itself. 
General Remarks on Fissure-veins—From what has 
been said in preceding paragraphs, it will be gathered that 
a lode may present many different features throughout its 
course. It may be massive in some places, banded and 
brecciated elsewhere. It may widen and contract irregularly, 
and may even pinch-out again and again. At the same 
time it may be accompanied by parallel veins or lodes, some 
of which may be independent, while others may be off-shoots 
or branches, which, after continuing their courses for longer 
or shorter distances, may again converge and rejoin the 
parent lode; or, instead of doing so, they may gradually thin 
out either simply or by subdividing into a complex of veinlets 
and threads. Both walls may be well defined throughout ; 
or one, usually the hanging-wall, may be rendered indistinct, 
either owing to the multitudinous fissuring of the rock, or to 
the abundant dissemination of mineral matter through the 
pores and capillaries of the “country,” or to the metasomatic 
replacement of the latter. Or dissemination and replacement 
together may succeed in obliterating both walls. On the other 
hand, many lodes are wonderfully regular, continuing between 
