Economic Geological Deposits. — Cvosby. 2AU 
cupied the great valley was at or near sea level, it is obvious 
that the region of the great valley has also risen, since it is 
now high and dry. The Inyo earthquake of 187,2 may have 
been due to a slipping along the normal fault zone of the east- 
ern escarpment, which was. perhaps, accompanied by an up- 
ward movement of the crest directly west. 
[To be concluded in next number. | 
A CLASSIFICATION OF ECONOMIC GEOLOGICAL 
DEPOSITS BASED ON ORIGIN AND 
ORIGINAL STRUCTURE. 
By W. O. Chosby, Boston, Mass. 
Introduction. 
The title of this paper might be otherwise expressed as the 
enumeration and brief description in natural order of the va- 
rious modes of origin and occurrence of useful minerals and 
rocks. A strictly natural classification on economic lines is, 
of course, impossible; simply because nature has shown no 
special regard for our economic distinctions. The position 
of a rock in the natural classification is essentially the same, 
whether it contains one grain, one ounce, or one pound of gold 
to the ton. The economic classification must, in every instance. 
be a fragmentary scheme, lacking the completeness and per- 
fect coordination or symmetry which we recognize or believe 
to be recognizable in nature; for it represents a body of 
knowledge having arbitrary or artificial and shifting bound- 
aries. A mineral which is valueless to-day may find a useful 
application to-morrow, and thus, perhaps, introduce into Un- 
economic classification a new type of deposil ; and in like 
manner the deposits of -a particular type may be dropped from 
the economic scheme, if the substance which they afford lie 
supplanted in its relations to human welfare by some other. 
The most nearly ideal plan would, it is believed, be a com 
pletely elaborated natural or scientific classification, with a 
special mark to designate those deposits of present economic 
interest. The practical man. who often care- little for the 
general relations to the whole of tin- small part in which he 
*A paper presented before i he Geological Society of America, I »'•<•. '."•'. 
1893. 
