INVESTIGATION OF METALLIFEROUS ORES. 
By S. F. Emmons, Geologist in Charge. 
INTRODUCTION. 
In the years immediately following the organization of the United 
States Geological Survey its geological work was classed under two 
broad divisions, namely, general geology and mining geology. The 
primary object of the latter work was, by careful scientific studies of 
the most extensive mines and mining districts of the country, to 
gather together such an array of accurately determined facts with 
regard to the phenomena of ore deposition as would serve as a basis 
for generalizations, or laws governing the formation of metalliferous 
deposits. Incidentally it was expected that a demonstration of the 
correct geological structure and relations of the deposits in each indi- 
vidual district would prove of immediate practical value to those 
engaged in mining in that district, and serve as a guide to them in 
their explorations. This, however, was regarded as of secondary 
importance compared to the first object, since general laws are useful 
to mine owners the world over and are not confined in their applica- 
tion to the mines of a certain district. 
The commercial interest of mining industry was more directly sub- 
served by the collection of statistics of the mineral resources of the 
country, which was at first a branch of mining geology. As time has 
gone on and, with increasing pecuniary resources, the field of work 
of the Survey has widened, the above-mentioned classification of its 
work has been somewhat changed in title, as well as in the scope of 
the different divisions, but the main underlying principles have 
remained practically the same. 
The collection of mineral statistics is of direct commercial value to 
mining industry, which was readily recognized by the general public, 
and, direct and generous appropriations having been made for it, it 
lias become a special division. 
GENERAL GEOLOGY. 
Whereas in the early days but little could be done toward preparing 
•i geological map of the whole country, which is theoretically the prime 
abject of a geological survey, because of the want of the indispensable 
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