286 
VADOSE ORE DEPOSITION 
persons committed to a strictly igneous theory are loath to admit. 
This is a local phase; it has much broader aspects. The bonanza 
zone is properly to be considered not as a mere local phenomenon 
but as one of world-wide extent. The vadose zone of the ores 
may thus be viewed much in the same way as is the regolith, as 
having everywhere at its base a sub-zone of bonanza character, 
that in some places is sufficiently well-developed to be mined, but 
elsewhere often only feebly represented by ore-materials. The 
bonanza layer is the ultimate and maximum localization of vadose 
metalliferous materials of industrial importance. 
In bulk the ore-materials of the vadose zone of arid regions 
must many times exceed the volume occurring in the accessible 
zone beneath the bonanza level. One of the main results of an 
extensive inquiry recently instituted in Mexico, for the purpose 
of determining the probable persistence of ore-bodies in depth, 
clearly indicates that in the large majority of cases little is to be 
expected. Only in exceptional instances is the outlook sufficiently 
favorable to warrant the continued exploration for possible deep- 
lying ores. Similar, but less comprehensive, observations con¬ 
ducted in certain parts of western United States strongly point to 
like conclusions. In the dry regions present estimates place the 
total volume of ore in the vadose zone at about ten times greater 
than that of the profound zone. 
As bearing upon the immediate sources of the ore-materials in 
general these results are significant. They suggest that on the 
whole metalliferous materials are not segregated into ore-bodies 
so directly from the depths as it has been customary to suppose. 
They point to a larger importance of the metallic minerals diffused 
through the rocks and liberated by the latter’s disintegration. They 
also indicate a larger influence of the meteoritic augmentations to 
the earth’s supplies of metals as early advanced by Meyer,^^ and 
which later found strong support in the planetesimal hypothesis 
of the origin of our globe, as proposed by Chamberlin. These 
aspects of the subject I have also lately summed up.^® 
It is in the arid regions that complete data on this theme are 
to be obtained. 
From areas presenting large intrusive masses will doubtless 
24 Beitrage zur Mechanik des Himmels, p. 157, 1848. 
25 Carnegie Institute Yearbook, No. 3, p. 208, 1905. 
26 Trans. American Ins. Mining Eng., Vol. XL,I, p. 139, 1910. 
