go Joseph LeConte— Genesis of Me etalliferous Veins. 
supply of material to the soos dates indeed we resort to 
.occult forces of which we kno thing. 1 subterranean 
waters are in movement—ina cibotliBion which completes itself 
only by issuance on the surface. The movement may be slow 
or rapid. The issuance may be, as a panes moisture 
evaporating on the surface, or may be in the form of springs of 
e 
that for two reasons. In the first phe if the su a of water 
is abundant the percentage of soluble matter may be too small 
to deposit. We see illustration of this in the phenomena of 
the forming and filling of limestone caves. At one time when 
the supply of water flowing through them was abundant, they 
were hollowed out by reine “bat now that the water is 
reduced to droppings they are filling by deposit. In the second 
place, rapid movement of abundant water is unfavorable for 
deposit in conduits, because the cooling on approaching the 
surface will be too slow. The water will carry its own tempe- 
rature with it instead of borrowing it wholly from the adjacent 
rock. For these two reasons therefore, decided springs are apt 
to deposit only on the surface, where, only, the cooling is suffi- 
cient and where aepeet also takes place by evaporation and 
oxidation. In a all subterranean waters are in movement 
and such apees, is necessary to bring sufficient supplies of 
feebly soluble matters. Also, all or nearly all circulating wa- 
ters terminate their journey on the surface. Whether their 
ded fountains, wee the conduits or waterways are most apt to 
be filled by deposi 
Again, Dr. Sa baee thinks that metamorphic rocks de- 
rive their vein-contents from the igneous rocks in their vicin- 
ity. We on the contrary regard the igneous rocks as contrib- 
uting not so much the materials as the heat necessary for their 
solution. There is probably no substantial difference in the 
chemical composition of igneous and sedimentary rocks. They 
are convertible into each other me are often so converted by 
alternate disintegrations and re-fusions, 
Again, Dr. ee thinks ‘that solfataric waters at Sul- 
phur Bank and elsewhere deposit only at the surface and in 
contact with the atmosphere—that these do not fill their con- 
oe and thus form veins, and therefore we are not to look to 
