230 ORE-DEPOSITION IN TRUNK-CHANNELS 
4 
account of these very conditions they doubtless do not take up 
metals on their way up to the surface of the ground again. The 
non-soluble character imposed during the passage of metallic 
substances through the profound region evidently remains so 
under all ordinary increases of temperature which they are likely 
to encounter. 
On the other hand ascending juvenile waters appear to part 
with all or nearly all of their ore-forming materials long before 
they reach the normal groundwater-line and the confines of 
of the vadose zone. The locus of principal ore-deposition appears 
to be near the bottom of the main channels through which the 
vapors and waters find exit from the magmatic masses. Only 
long afterwards when the ore-bodies are brought to the surface 
of the ground through the general erosion and lowering of up¬ 
raised belts of the country are they made accessible to man. 
Since in the one case there is notable rock-solution and in the 
other rock cementation it follows that the ore forming tendency 
of the trunk-channels of the vadose zone and those of the pro¬ 
found zone are directly opposed. In the light of the most recent 
tests regarding the locus of maximum ore-deposition the theory 
of trunk-channel localization of ores, as advanced by Van Hise 
and others, needs to undergo considerable modification before 
it can be made acceptable. If under normally wet-climate con¬ 
ditions the greater part of vadose trunk-channels must be re¬ 
garded as lines of ore-depletion rather than of ore-enrichment, 
the subject assumes added interest when it is considered that in 
arid tracts of the globe the vadose zone, as recently shown, 
attains enormous thicknesses and acquires vast importance in 
mining. 
