848                           MINEBAL RESOUBCES, 1914—PART I.
	The enumeration of placer mines is less satisfactory than that of deep mines, because some of the operations are only temporary and individually small, and because the production is frequently by transitory miners not regularly working placer ground. The unit, so far as possible is, however, as for deep mines, not the operator, but the mining claim or group of claims. Number of producing mines in 1914, by States and Territories .a
	The table stows the number and distribution of mines producing gold and silver in the United States and Alaska. With the exception of (1) some of the Michigan copper mines, (2) all zinc mines in the Eastern and Central States and a few in the Far West, and (3) all lead mines of the Central States (except a few in Illinois and south­eastern Missouri), practically all mines producing copper, lead, and zinc in the United States and Alaska produce gold and silver also. The table, therefore, with these exceptions, is a table of mines pro­ducing these five metals. It also includes certain mines producing oxidized manganese iron fluxing ores of Colorado, Utah, and else­where, whose ores contain small quantities of precious metals, especially silver, and are smelted as flux. Comparisons with the corresponding figures for 1913 show a net total decrease of 303 producing mines, following decreases also in 1912 and in 1911. This decrease may be due in part to consolida­tions, in part to closer estimates for placer operators, and in part to actual falling off in number of active producing properties caused, perhaps, by failure of prospecting to develop sufficient producing mines to take the place of mines no longer on the producing list.