208 PROCEEDINGS OF SECTION GC. 
necessary to fall back on such conclusions as can be drawn 
from theoretical considerations and general observations. 
It is well known that no rocks are absolutely impervious 
to water, while many kinds are, comparatively speaking, 
porous. Uncemented conglomerates, sandstones, tuffs, and 
other fragmentary rocks are the most porous, and these 
rocks permit of a most thorough leaching action by waters 
passing through them. Many rocks are traversed by joint 
planes, planes of fissility and sedimentation, which afford 
openings through which water may travel. The massive 
eruptive rockscontain cracks and joints caused by shrinkage 
during cooling, while all rocks are traversed by the larger 
fault fissures. It should be noted that the massive eruptive 
rocks which are believed to be the richest in their metallic 
contents, and those from which we would naturally suppose 
the great majority of ore deposits to be derived, are the least 
adapted to the leaching process. It is true they frequently 
contain joints and cracks, but these comparatively larger 
visible cracks expose only a very small proportion of the 
whole rock to the action of circulating waters. If the 
minute metallic contents of these massive rocks are leached 
out by circulating waters to any appreciable extent, almost 
the whole work of leaching must take place in the extremely 
small invisible openings, such as cleavage cracks, &c. We 
can hardly form any conception of the rate of flowage 
through such minute openings. The ordinary laws of 
Hydrostatics cease to operate for flowage through capillary 
openings. Van Hise,* in his valuable treatise entitled 
“Some Principals controlling the Deposition of Ores,” 
shows that flowage in capillary openings is directly propor- 
tional to the pressure and to the 4th power of the radius 
(the square of the sectional area) of the opening. While in 
openings of larger than capillary size the flowage is propor- 
tional to the square root of the pressure, and as the square 
of the radius (or as the sectional area). This proves that in 
the small capillary openings flowage decreases very much 
more rapidly with decrease in pressure or sectional area 
than in openings of larger than capillary size. For 
example, in the case of super-capillary openings the flowage 
through a crack 1mm. wide will be one-tenth of that 
through a crack 10 mm. wide, and one-hundredth of that 
through a crack 100 mm. wide. But in the case of capillary 
openings the flowage through a crack -001 mm. wide will 
be one-hundredth of that through a crack -01 mm. wide, 
and one-ten thousandth of that throughacrack -1 mm. wide. 
* Trans. Am. Inst. M. Eng., 1890. 
