emmons] INVESTIGATION OF METALLIFEROUS ORES. 19 
in Europe, as well as in this country, and all have been gathered 
together and published in a special volume by the Institute of 
Mining Engineers. Such publications are not intended to be final. 
Already, since the appearance of the above-mentioned volume, impor- 
tant modifications of the views therein presented have been suggested, 
and further important additions to our knowledge of the subject are 
to be expected from the constantly increasing amount of accurate 
work that is being done every year by the Survey. 
A brief review will now be given of the published results of this 
work, together with a statement of that which is in progress but has 
not yet reached the stage of publication. 
Economic Publications on Metalliferous Deposits. 
During the year 1901 there was published in the Bulletin series, by 
F. L. Ransome, a volume (Bulletin No. 182) on the Economic Geology 
of the Silverton Quadrangle, which belongs to the second class of 
economic publications mentioned above — that is, economic examina- 
tions incidental to areal work. The Silverton quadrangle had already 
been areally surveyed hy a party under the charge of Whitman Cross, 
who has been engaged for a number of j^ears past in making a geo- 
logical study of the whole region of the San Juan Mountains in south- 
western Colorado. Under the system adopted by the Survey, as each 
fraction of a degree — in this case one-sixteenth, or fifteen minutes — is 
surveyed topographicaltyand areally, the results are published in folio 
form, and when mining interests justify it an economic geologist is 
detailed to work either with the areal party or following it and to make 
a special study of the mines and ore deposits of the whole area. Such 
a study had already been made by C. W. Purington of the mines of the 
| Telluride quadrangle, and his results were published as a special 
paper in the Eighteenth Annual Report. 
The whole San Juan region is rich in ore deposits, occurring to an 
unusual degree in well-defined fissures and also in more irregular 
forms, called stocks or chimneys, which carry values in gold, silver, 
i' copper, lead, and zinc. The Silverton quadrangle, which lies next 
east of the Telluride, contains, like the latter, a large number of 
important mines within its area. In many of these the richer ores or 
bonanzas have been extracted and they are, for the time being, aban- 
doned; others, such as the Camp Bird, Silver Lake, and Tom Boy, are 
in active operation. The record obtained from the latter is naturally 
the most valuable, but the former also afford data of importance. 
IThis report contains not only a statement of the geological relations 
of each important deposit in the area which must prove of practical 
value to those engaged in mining there, but some very valuable gen- 
tliijeralizations which Mr. Ransome was able to make from the lode 
ilmi fissures and stocks or masses, also a statement of their contained min- 
erals and their paragenesis and origin, as well as important contri- 
butions to the new theory of enrichment of ores by descending waters. 
