DISTRIBUTION. Ore deposits are not confined to any particular geological horizon, although the meehanically formed and some of the surficial ones are commonly of Pleistocene and less often Tertiary age. 1tt the United States ore deposits are widely distributed, but, owing to their fre quent association with igneous rocks, they pre tbaninate in the Cordilleran region, Black Hills, and the Appalachians, where igneous activity has been most pronounced. In other areas their accu mulation scents to be chiefly the result of meteoric waters. (told and silver ores are chiefly restricted to fissure veins, and hence predominate in the Cor dilleran region. although additional vein deposits of gold are known in the Black Ilills, Southern .Appalachians. and Alaska.
Copper ores are known in large deposits in Keeweenaw Point, Mich., Bisbee, Ariz., and Butte, The Paleozoic limestones of ..)lissouri, and the region covering the contact point of Iowa, Illinois, and Wisconsin, contain both lead and zinc, and large zinc deposits are mined in the Cambrian limestones of northwestern New ,Terse'. The hematite iron ores of the Lake Superior region are the largest deposits in the world, hut others are known in the Silurian of lhe Ap palachian region. and the metamorphic rocks of the 'Highland region. For further details rvgard ing the distribution of ore deposits, wee On.o, StbvEn, Coemat, etc.. also the paragraphs on min ing, under the different countries.
Bint.foonAPHY. General works: Kemp. Ore Deposits of the Fnited Mates and ranada (New York, 1900) Whitney. Metallic Wealth of the United Rtates (Philadelphia, 1854) : Phillips, Treatise on Ore Deposits (London, ISS4) Tarr, Eronomie Geology of the United Slates (New York, 1895) ; Fuchs and De Launay, Trait, des gites mint'raux ct metallIferes (Park, 1S93); Beck, Lehrbuch der Lugerstuttenkunde (Berlin, 1(100) ; Von Cotta, ore deposits. trans. by Prime
(New York. 1870). Works dealing chiefly with genesis of ore deposits: Crosby, "A Classifica tion of Economic Geological Deposits Based on Origin and Original Structure," in the Ameri can Geologist (Minneapolis, 1899) ; Emmons, "The Structural Relations of Ore Deposits." in the Transactions of the American Institute of Min ing Engineers. vol. xvi. (New York, 18861 ; Em mons, The Genesi, of Certain Ore Deposits," ibid., vol. xv. (ib., 1SS5) Groddeck, Die Lehre von den Lagerstiitten der Erze (Leipzig. 1879) : Kemp. "An Outline of the Views Held To Day on the Origin of Ores," in The 31ineral Industry, vol. iv. (New York, 1895) ; Posepny, "The Genesis of Ore Deposits," in the Transac tions of the Ameriean Institute of Mining Engi veers (ib- 1893) ; Vogt. "The Formation of Eruptive Ore Deposits." in The Hincral Indus vol. iv. (ib.. 1895) : Vogt, die rela tive Verbreitung der Elemente, besonders der •Schwermetalle, and fiber die Concentration des fein vertheilten :Metallgehaltes zur Erzlager stiitten." in the Zeitsehrift fiir praktische Geo/o gle (Berlin, 1S05-99) : Penrose. "The Superficial Alteration of (Ire Deposits." in Journal of Geol ogy. vol. ii. (Chicago. 1894), an excellent general article: Weed. :Metamorphic and Other Ore Deposits Year Igneous Contacts." and "Vein Enrichment by Ascending Alkaline Waters." in Engineering and Mining Journal. vol. lxxiv. (New York. 1902). Also many articles in the Tran.s aetimis of the American Institute of 3Iining Engineers (New York. 1900-02).