358 The American Geologist. June, looi. 
metals in these rocks is due larg-ely to the same concentration 
which produced the existing ore bodies. 
The analyses mentioned were made for the express ])urpose 
of supplying' evidence to the theory of the general diffusion of 
metals in rock masses. Winslow's liypothesis* is that in the 
Ozark region the rocks have suffered enormous denudation, 
and consequently the metallic substances that were diffused 
through the portion eroded have settled down, and have been 
redeposited in the constantly lowering zone at or near the 
ground surface. 
Curiously enough for this hypothesis, along the summit of 
the Ozark dome, where decomposition and denudation have 
been greatest (by some 4.000 feet or more than at the margins) 
there afe practically no ore bodies of consequence. The rich- 
est and most extensive deposits are at the very base of the up- 
lift, in a district which has not only suffered a minimum amount 
of denudation, but which has not been removed more than the 
northern part of the state of ^Missouri, where no deposits what- 
ever occur. 
In a verv localized form the same hypothesis is claimed 
to be applicable to true fissure veins. This phase of the subject 
has 1>een lately emphasized by Weedt in the consideration of 
the gold and silver deposits of Montana. This author also cai^s 
special attention to the ore bodies of the Australian Broken Hill 
Consol mine of Xew South Wales, as described by Smith, $ and 
to the Aspen district of Colorado, described by Spurr. § He 
says : "Active degradation favors the accumulation of enrich- 
ments, while prolonged degradation of a region, resulting from 
physiographic revolutions, may result in successive migrations 
of material and the accumulation in a relatively shallow zone 
of the metals derived from many hundreds, and possibly thou- 
sands, of feet of the vein worn away in the degradation 
of the land. Climatic conditions, rainfall or aridity, warmth 
and rapid alteration of vein fracture are agents. affecting sur- 
face weathering, and hence, also, enrichment. 
"Active degradation of a region, that is, rapid weathering, 
favors enrichment by the quickness with which it removes the 
upper already leached part of the vein, so that a large amount 
• Missouri Geol. Stir., toI. vii, p. 469, 1894. 
■;■ Trans. American Inst. Min. Eng., vol. xxx, 1900. 
+ Trans. American Inst. Min. Eng., vol. xxvii p. 69, 1896. 
§ V. S. G'^.ol. Surv., Mon. xxxi, 1898. 
