DEPTH OF ZONE OF FLOW IN THE EARTH’S CRUST 117 
consideration in this paper, it is clear that if these are crushed in, 
smaller cavities will survive even in the crushed mass of rock 
formed by the collapse of the walls of such a cavity, and will afford 
ample passage for solutions, vapors, etc., and, therefore, provide 
the conditions required for the deposition of mineral deposits of 
the replacement type at least at the great depths in question. 
SUMMARY OF CONCLUSIONS 
1. The calculations which have been made as to the depth 
below the earth’s surface at which all cavities in the earth’s crust 
would be closed by plastic flow, based on the crushing strength 
of rocks at the surface of the earth, are erroneous. 
2. At ordinary temperatures but under the conditions of hydro- 
static pressure or cubic compression which exist within the earth’s 
crust, granite will sustain a load of nearly 100 tons to the square 
inch, that is to say, a load rather more than seven times as great 
as that which will crush it at the surface of the earth under the 
conditions of the usual laboratory test. 
3. Under the conditions of pressure and temperature which 
are believed to obtain within the earth’s crust, empty cavities may 
exist in granite to a depth of at least 11 miles. These may extend 
to still greater depths, and if filled with water, gas or vapor, will 
certainly do so, owing to the pressure exerted by such fluids or 
gases upon the inner surfaces of such cavities or fissures. 
4. Since the existence of open spaces through which aqueous 
solutions, vapors, or gases can traverse a rock is a factor in the 
development of mineral veins and replacement deposits, such veins 
and deposits may be formed within the earth’s crust to a depth 
of at least 11 miles below the surface. That is to say, they may 
extend to a much greater depth than it is possible to follow them 
by any method of mining now employed. 
DESCRIPTION OF PLATES 
PrArr 
Fic. a.—Shows a column of Solenhofen limestone (Exp. 359) which has 
been submitted to a pressure equivalent to a depth of 15 miles within the 
earth’s crust for 2 months. The steel tube has been partially removed so as 
