28 H.C: COOKE 
to solve the problem attacked. The data at hand dealing with 
the secondary enrichment of silver are scarcely complete enough to 
make such verification of this work at the present time. The full 
solution of the problem would require (a) approximately accurate 
estimates of the proportions in which pyrite, primary silver sulphide, 
and secondary silver sulphides are present, in a large number of 
deposits; () more analyses of mine waters, and especially of waters 
from the same mine at different depths; (c) further observations 
on the changes in chemical and mineralogical composition of lodes 
with depth; (d) accurate analyses of the thin veinlets of secondary 
material that cut primary sulphide ores; (e) in cerargyrite deposits, 
analyses of the waters at top and bottom of the cerargyrite zone. 
Such data would at once render it possible to determine whether or 
not the processes of the secondary enrichment were subject to 
factors other than those mentioned in this paper. 
In conclusion, the writer wishes to express his thanks to Pro- 
fessor W. H. Emmons, who suggested this research and generously 
placed at the writer’s disposal his invaluable fund of practical 
information on the subject. He also wishes to make grateful ac- 
knowledgment to Professor Julius Stieglitz for much kind assistance 
and valuable criticism; and to Mr. A. D. Brokaw for many useful 
suggestions. As regards the work of this paper, the writer recog- 
nizes the incomplete and, as it were, qualitative nature of many of 
the results obtained; this, however, was unavoidable on account of 
the preliminary nature of the work, the large field covered, and the 
limited time at his disposal. It is his aim to investigate more 
accurately in the near future many of the problems as yet but 
incompletely solved. 
