2)2 PROCEEDINGS OF SECTION C. 
water must utilise the whole available sectional area of the 
Openings connecting the two regions, flowage must also 
take place in the same general direction through all open- 
ings of the second and higher orders throughout the range 
of the travelling water. Though all available openings 
must be utilised, flowage through them will be inversely 
proportional to their resistance, and of course the amount 
passing through individual openings of the third and higher 
orders must be extremely minute, and the rate of flow must 
be small. 
To form a conception of the amount of water likely to 
traverse the smaller openings in the denser rocks, let us 
picture a block of granite, say, 10 feet cube, surrounded by. 
a water space varying from nothing to 1 mm. in width. 
A difference of hydrostatic head, between the water at each 
side of the block, that would be quite sufficient to determine 
a distinct and even rapid flow around the block, would 
evidently determine only the very smallest imaginable 
amount of flow through the minute openings of higher 
orders within the block; which openings we must, however, 
theoretically admit to bear some share in the transfer of 
water from one side of the block to the other. 
It is further evident, from the above illustration, that 
there must be a constant interchange of waters between the 
_ openings of the various orders, and it is to this agency that 
we must attribute the leaching and cementing action of 
underground water. Unfortunately, we have not yet suffi- 
cient data at our command to form any approach to an 
accurate estimate of the amount of this circulation through 
the more minute openings, so that we have room for very 
decided differences of opinion as to its efficacy in producing 
the more marked phenomena, such as ore concentration. 
To resume the larger question of the nature and causes 
of the general circulation—we have seen that difference in 
temperature between the ascending and descending columns 
is the main force producing circulation, and I propose here 
only to discuss the circulation which is produced by this 
means. 
Imagine, then, all these openings in the system of blocks 
within blocks to be filled with water, and, further, suppose 
heat to be applied to the lower porton of this system of 
water channels. The heat causes expansion in the water, 
and, therefore, movement; then, as the resistance of the 
small openings is so much greater than that of the large 
openings, the greater part of the flowage would be induced 
in the main channels, i.e., the heated water would rise to a 
