ii6 The American Geologist. August, 1902. 
1. Deep-seated zone, characterized by arsenopyrite, pyr- 
ite and pyrrhotite with other minerals subordinate. This tin- 
derHes the surface zone and reaches to depths not yet deter- 
mined. 
2. Surface zone, characterized by abundance of galena, 
blende and chalcopyrite. 
The upper sulphide zone is commercially the most impor- 
tant. 
The occurrence and shape of the ore pockets point to de- 
position from downward moving waters. A favorite place for 
the deposition of sulphides has been at the intersection of two 
joints, generally a steeply-dipping and more flatly-dipping 
one. In many cases the ore has been deposited entirely in the 
bottom of the trough formed by such intersection without any 
considerable amount being deposited beneath the roof which 
the intersecting joints have formed. If the waters had been 
ascending the solutions would naturally have converged under 
this roof and would have there been precipitated more easily 
than in the overlying trough, but this the author has not ob- 
served. Other facts are cited to prove the theory adopted 
and advocated, viz., that the waters which produced the sul- 
phide ores were distinctly descending, and that descending 
waters alone have produced both the primary and secondary, 
the leaner and the richer ores. It is stated that the oxidized 
zone, the intermediate sulphide zone, and part of the upper 
sulphide zone are all being contemporaneously precipitated at 
the present time. 
The cource of these metals is believed to be the tonalyte it- 
self, and the other eruptives ; iron, lead, copper, zinc, antimony, 
silver and gold are known to occur in the dark-colored sili- 
cates of igneous rocks ; and the magnetite of the tonalyte may 
itself contain the other metals. The lead of the upper sulphide 
zone is not found in the lower sulphide zone, and is supposed 
to have been derived from surrounding rocks and, like all the 
other sulphides, to have been deposited by downward per- 
colating waters, the different belts of minerals occurring in 
the order of their relative solubility. 
As a practical conclusion, it is stated that the best veins 
in this district should be looked for in or near the tonalyte, and 
especially along the predominant steep east-northeast joint 
zones. 
