384 
VADOSE ORE DEPOSITION 
Hofer ® are not without value at the present time. The some¬ 
what similar classificatory schemes of Whitney,^® Grimm,New¬ 
berry and Phillips have important and suggestive features 
that cannot be well overlooked. 
By substituting for geometric shape tectonic form, shape still 
remains a very useful criterion in ore-classification. In the 
vadose zone, particularly in arid regions, among deposits of the 
main genetic group of ore-bodies the distinctions made may be 
advantageously adopted. To this further attention is directed 
in another place. 
The illustrations noted are those which among others have, 
in the course of professional work, come under my personal 
observation. When there are also good descriptions, reference 
is made to the literature. 
Complete cementation of rock-masses is not always an im¬ 
mediate consequence of their first consolidation. Geologic forma¬ 
tions may remain porous indefinitely; the Peter Sandstone of 
the Upper Mississippi Valley has been a good aquifer since Cam¬ 
bric times. Than this the filling of the interstices of the com¬ 
ponent grains of a rock is commonly more rapid. Under favorable 
conditions, of which impondment of groundwaters is not the 
least important factor, metallic salts form part of the infiltration, 
and disseminated ore-bodies often result. 
When local impondment-conditions prevail in porous sand¬ 
stones, ore-materials often accumulate, as in the “Silver Reef” 
of Utah. Elsewhere, through dolomitization of limestones certain 
layers are rendered quite porous, as in the moist districts of 
southeast Missouri. The scoriaceous upper surfaces of lava- 
flows, when buried, constitute layers through which the surface 
water readily circulates, as in the case of the amygdaloidal copper- 
deposits of Lake Superior. 
In arid regions, sandstones especially are liable to be extremely 
porous, and in the vadose zone to contain ore-materials in appre¬ 
ciable or even workable volume. This is particularly true of 
the Red-Beds of western United States, that comprise many 
thick beds of sandrock. The Red-Beds formations extend over 
9 Zeitschrift fiir practische Geologic, 1897. 
10 Metallic Wealth of the United States, 1854. 
11 Die Lagerstatten der nutzbaren Mineralien, 1869. 
12 School of Mines Quarterly, Vol. I, p. 27, 1880. 
13 Treatise on Ore Deposits, 1884. 
