362 The American Geologist. J"'"^- ^y*" 
sheet would ordinarily carr\- the decomposed materials far 
from the neighborhood. 
The general metallic content carried by circulating waters 
would doubtless accomplish the same result of secondary en- 
richment of lean veins, but it would certainly be through other 
openings than that in which the original vein was formed. 
In the particular examples cited by Weed''' of the Mollie 
Gibson and Smuggler ore bodies and bonanzas, the enrichments 
are along the lines of secondary faulting and the alterations are 
only in the immediate vicinity of these later fractures. Many 
other similar examples might be mentioned. 
The immediate practical importance of the distinction is 
perhaps not so great at the present time as is the fact that tlu- 
plausibility of the hypothesis at first glance being so evident 
is likely to lead often to imtrustworthy conclusions. 
The conclusion seems inevitable that with the exception of 
possibly a few isolated unimportant instances ore concentration 
does not generally take place through surface decomposition 
of rock masses, in areas such as the Ozark lead and zinc re- 
gion. As in the case of petroleiuii, if it be assumed that all 
rocks at all times contain ample supplies of metallic salts in a 
diffused condition sufficient for the most extensive ore de- 
posits, and that tlie circulatory waters hold them at all times in 
solution to a greater or less but adequate extent, these musi 
be regarded general, always present conditions. But concen- 
tration of metallic salts into ore bodies must be admitted to be 
accomplished under special local conditions of geological struc- 
ttire. quite inde])endent of all rock decomposition and land 
degradation. 
* Trans. American Inst. Min. Eng., vol. xx.y, 1900. 
