116 FRANK D. ADAMS 
the size of a cavity is one which must be considered in this connec- 
tion. In the accompanying paper Mr. King has investigated this 
subject mathematically and shows that in the case of any given 
rock a pressure might be reached which would be sufficient to 
crush in larger cavities, but the collapse of the walls instead of 
leading to the complete closing of the cavity in question would 
merely result in the formation of a number of smaller spaces, which 
would remain open permanently or which could only be closed by 
a greatly increased pressure. 
.This factor has. been eliminated in the present investigation by 
having the holes in the case of all the experiments identical in size 
and relatively small. 
It is the depth to which these smaller cavities and passages will 
remain open that is the really important one in connection with the 
question of the depth to which mineral deposits may extend. For 
although a great fissure vein may have been developed by the 
filling of a great fissure, it is considered by some authorities that 
the crystallographic force of the growing minerals filling the vein 
has had an important influence in opening up a comparatively 
narrow fissure, thus making a relatively wide vein in what was 
originally a comparatively narrow crack. But whether this be 
so or not, a class of deposits which are much more numerous and 
more important than “true fissure veins,” namely replacements, 
do not require any originally wide fissures for their development, 
but are formed by the passage of mineralizing solutions or vapors 
through narrow cracks or fissures, which serve merely to give such 
solutions or vapors under high pressures a passage into and through 
the rock, which they attack and alter and in which they deposit 
their burden of ores and other valuable minerals by a process of 
replacement. All, therefore, that is needed for the formation of 
such deposits are very narrow cavities or fissures to give the mineral 
bearing solutions access to the rock in which the ores are to be con- 
centrated. Many deposits in shear zones and shattered strips of 
rock are of this character, as well as other replacement deposits 
in which the lines of the original fissures are now entirely obliterated. 
Whatever, therefore, may be the fate of great yawning chasms 
if these are formed within the earth’s crust at the depths under 
