Ore Formation by Surface Decomposition. — Kcyes. 361 
and that the leached substances from near the grtjund surface 
are being carried through faults, joints and cracks downward 
to lower levels. In addition to all this there must be special 
local geological conditions to be satisfied before ore bodies 
can begin to form. 
There is a parallel example in the case of petroleum. Next 
to water, we now know that rock-oil is perhaps the most abund- 
ant substance circulating in the earth's crust. The Waterlime 
formation of Ohio and certain dolomytes of the Mississippi 
valley contain in each 500 feet of thickness upwards of 2,500,- 
000 barrels of oil to the square mile. The oil contained in only 
three townships would thus be more than the total amount 
which has up to the present time been taken out of Pennsylva- 
nia and New York fields. In order to have an area econom- 
ically productive a peculiar association of geological structures 
and conditions must exist. There must be a reservoir in the 
form of a porous or cavernous bed, a non-porous cover as af- 
forded by a shale stratum, and a bowing up of the strata such 
as is presented by an anticline. The absence of anv one of these 
precludes the accumulation of oil bodies. So in connection 
with the ores the conditions and structures may all be present 
but one and yet there will be a failure of ore bodies. 
In the more special case, in which a concentration has al- 
ready well progressed, as presented by a mineral vein or a 
lean ore vein, where enrichment has taken place below the 
zone of w^eathering through downward flowing currents, it 
does not appear probable that the ores from the upper part of 
a vein can be considered as furnishing the enriching materials, 
for the lower portion. As openings, fissures of any kind are 
at best very ephemeral in character. In no instance can they 
be regarded as forming open water passages for any consider- 
able period of time. They must be completely closed up long 
before surface degradation has advanced to any appreciable 
extent. 
New fissures may open up in the rock, new fault move- 
ments may take place, new cracks may be formed, through 
which metalliferous solutions may find access to the old mineral 
vein or lean ore sheet, but only in exceptional cases would ma- 
terial from the upper part of a vein find lodgement lower down 
in the same vein. The waters afifecting the surface of an o'c 
