12 = Joseph LeConte—Genesis of Metalliferous Veus. 
ant waters coming up in bold springs deposit mainly at the 
surface. 
are formed by deposit of soluble matters from superheated 
waters, coming up from great depths, and slowly losing heat 
d pressure, then the level at which deposit will commence 
tinue thereafter to the surface. On the one hand, the percentage 
e so small (either because so little bas been met with, or 
because the waters are too abundant and rapid-moving) that de- 
posit will take place only on the surface by drying and oxida- 
tion; on the other hand, the water may be so saturated when it 
ut metallic matters are eed sparsely and irregularly 
distributed in the country rock, and t 
surface. e have thus far supposed all the materials derived 
from the lowest depths only. But this is not true. Contribu- 
tions may be added at every step in the upward course by trib- 
utary waters from the wall rock. Whether these waters increase 
or decrease deposit will depend on their percentage of metallic 
freight as compared with that of the main up-coming stream. 
On the one hand, it is more likely to diminish it, because super- 
ficial waters are less apt to contain metallic contents than deeper 
waters; but, on the other hand, it may sometimes increase it by 
cooling more quickly the ascending waters. Again, we have 
supposed the deposit to take place only by loss of heat and 
pressure. This is doubtless the most obvious and widely occur- 
Ting cause; but there are also, as we have already shown, many 
