ORE DEPOSIT THEORIES. 211 
of the difference in temperature which may be produced 
by this means, but it is none the less certain that some 
difference must exist. The heat engendered by orogenic 
movements in the earth’s crust or by intrusive masses of 
eruptive rock must be the means of causing great differences 
in temperature between the ascending and descending 
columns. In such cases as these, the force producing circu- 
lation may be very great indeed. 
The Nature and Direction of Underground Flowage. 
The exhaustive treatment of this portion of the subject 
is beyond the scope of this paper. We are promised a full 
consideration of the phenomena in a treatise by Van Hise, 
to be published as a monograph in connection with the U.S. 
Geological Survey. Meantime, Professor Van Hise has 
given us a short explanation of his views in the paper 
already cited. I must confess, however, that I am unable 
fully to follow the distinguished geologist’s reasoning in his: 
abridged account, and must therefore await the appearance 
of the complete treatise. In the following short explana- 
tion I have presented the matter in a slightly different light, 
and attempted to show, briefly, what I believe to be the main 
causes which must control underground flowage. The 
results of my reasoning are identical with those of Van 
Hise. 
For the purpose of understanding the nature of under- 
ground flowage, we may imagine. the whole crust of the 
earth to be divided and sub-divided into an _ infinite 
number of blocks by the openings in the rocks. Thus, 
openings of the first order, such as the great fault fissures, 
would cut up the crust into a number of large blocks of the 
first order; openings of the second order, such as the 
smaller fissures, joint planes, &c., would sub-divide the 
blocks of the first order inte a great number of blocks of the 
second order; and further, openings of the third and higher 
orders, such as bedding planes, cleavage cracks, and the 
spaces between the grains, would split up the blocks of the 
second order into an innumerable number of minute blocks 
of the third and higher orders. This picture will give a 
sufficiently accurate notion of the distribution of the 
openings in rocks for the purposes of the present brief theo- 
retical inquiry into the general movements of underground 
water. 
Now, let us imagine water to flow from one region to 
another. The great bulk of the flowage would no doubt 
take place through the large fault fissures, &c., but since the 
