U>6 The American Geologist. March, 1896 
gests the following theory for this phenomenon: "The evi- 
dence of faulting and of the thin sheeting of the country- rock 
is there so clear that the explanation at once presents itself, 
that this appearance arises from the fad that the deposits are 
partly a filling in of interstitial spaces and partly a replace- 
ment of thin sheets of country rock — ." 
To the writer it seems more probable that instead of open 
lissures the process began with a crushed zone. That the vein 
matter was deposited as the solutions removed the crushed 
material, leaving at no time large empty spaces comparable in 
size to those now occupied b} r the great masses of quartz fre- 
quently met with. When large bunches of massive quartz 
occur 20 to M feet thick it seems incredible that merely fault- 
ing should have left empty spaces of such magnitude at the 
great depth at which they must have been formed. It seems 
more reasonable that the amount of crushing was greater in 
some places than in others, owing to divergent or intersecting 
Assures, allowing freer access of the mineral bearing solutions 
and a consequent more complete removal of the crushed mat- 
ter. The fact that most well defined fissure veins show a 
seam of clay between the quartz and the wall points plainly to 
the line along which additions to the vein must be made. Em- 
mons* remarks again that "Ore deposits are to a large extent 
the actual replacement of the country rock by vein materials 
and that the filling up by those materials is rather that of in- 
terstitial spaces than what might properly be considered open 
cavities." 
The frequent great regularity of the walls of fissure veins, 
especially along contacts, might be considered as an argument 
against this view, but it is rare that both walls are regular 
and the replacement would naturally be largely confined to the 
one more~easily fractured and penetrated by the solutions, as 
in the veins between diabase and slate. Where extensive oro- 
graphic movements are taking place the irregularities of the 
fissure must be more or less planed down, resulting in a mass 
of clay and broken rock, and that only in exceptional instan- 
ces could the strain be such as to open and maintain fissures 
five to twenty feet wide and hundreds of feet in extent during 
the protracted interval necessary for the deposition of the 
*Trans. Am. Inst. Mining Eng.. vol. xvi. 
