292 Tug American (jreoloyisf. NOvembor, i.h95 
the lead district are nuiuerous undulations of the strata. 
These flexures were doubtless the chief agent in the production 
of the crevices. As the strata were slowly elevated the heav- 
ily bedded limestones were fissured in a direction parallel to 
the axis of elevation and crevices more or less open were 
formed. In a direction at right angles little force was exerted 
and the beds were simply fractured, producing the narrow 
north and south fissures. It is also possible that the latter 
may be due to the contraction of the rock as it became more 
compacted. 
It is to be noted that the ore deposits of this region do not 
occur as fissure veins of indefinite extent in depth, but are in 
what are known as "gash veins" of limited extent and confined 
to one rock series. 
F/'lh')i(/ of fhe crevices. Two opposite views are at present 
held concerning the source whence veins have derived their 
metalliferous contents. (1) It is claimed on the one hand 
that the minerals have been deposited from hot solutions rising 
through fissures from profound depths. The solvent power of 
such waters would be great on account of the temperature and 
pressure, and they would thus be rich in mineral materials 
which would be deposited on cooling, or on relief from pres- 
sure. This is the view so ably advocated by Professor Franz 
Posepny in his recent paper on the "Genesis of Ore Deposits"* 
and it has among its supporters many eminent geologists and 
mining engineers. (2) Opposed to this ascension theory is 
that of lateral secretion, according to which the contents of 
the vein are derived from the wall rock itself instead of from 
unknown depths. A broad interpretation of the theory does 
not necessitate the derivation of the minerals from the rocks 
directly bounding the vein, but admits that they may have 
been leached out from a considerable distance on all sides. It 
supposes that there is a free circulation of surface waters 
tlirough crevices and porous strata, and consequently a ready 
transfer of solutions would result. These w^aters may traverse 
the rocks in any direction and may thus in cases rise and be 
said to come from below. Or, again, they may flow into the 
crevice either from the sides or from above. This broad con- 
ception of the lateral secretion theory has much in common 
with the one first named. But it ditfers from that, however 
*Trans. Am. Inst. Ming. Eng., vol. xxiii, p. 197, 1894. 
