54 KEMPS ORE DEPOSITS. 



II. Deposited from Solution. 



1. Surface precipitations, often forming beds, 



and caused by 



(a) Oxidation. Bog ores. Ferruginous oolites, as 



in some Clinton ores. 1 



(b) Sulphurous exhalations from decaying organic 



matter etc. (Pyrite.) 



(c) Reduction, chiefly by carbonaceous, organic 



matter. (Pyrite from ferrous sulphate.) 



(d) Evaporation, cooling, loss of pressure, etc. 



(Hot spring deposits, as at Steamboat 

 Springs, Nev. 2 ) 



(e) Secretions of living organisms. (Iron ores by 



algae. 3 ) 



NOTE. These same causes of precipitation operate in subter- 

 ranean cavities, although not again specially referred to. 



2. Disseminations (impregnations) in par- 



ticular beds or sheets, because of : 



(a) Selective porosity. (Silver Cliff, Colo., silver 



ore in porous rhyolite. 4 Amygdaloidal fill- 

 ings, as in copper-bearing amygdaloids, 

 Keweenaw Point, Santa Rita, N. M. 5 Im- 

 pregnations of porous sandstone, as at Silver 

 Reef, Utah. 6 



(b) Selective precipitation by limestone. (Lateral 



enlargements at Newman Hill, near Rico, 

 Colo. 7 ) 



3. Filling joints, caused by cooling or drying. 



(Mississippi Valley gash veins in part.) 



4. Occupying chambers (caves) in limestone. 



(Cave Mine, Utah. 8 ) 



1 C. H. Smyth, Jr., Amer. Jour. Sci., June, 1892, p. 487. 



2 G. F. Becker, Monograph XIII. , U.S. Oeol. Survey, pp. 331, 468; 

 Laur, Ann. des Mines, 1863, p. 421; J. Leconte, Amer. Jour. Sci., June, 

 1883, p. 424, July, p. 1; W. H. Weed, idem, August, 1891, p. 166. 



8 Sjogrun, Berg.- und Hutt. Zeit., 1865, p. 116. 



4 Clark, Engineering and Mining Journal, Nov. 2, 1878, p. 314. 



5 A. F. Wendt, Trans. Amer. Instit. Min. Eng., XV. 27. 



6 C. M. Rolker, idem, IX. 21. 



7 J. B. Farish, Proc. Colo. Sci. Soc., April 4, 1892. 



8 J. S. Newberry, School of Mines Quarterly, March, 1880. See also 

 J. P. Kimball,on Santa Eulalia, Chihuahua, Amer. Jour. Sci., II., xlix. 161. 



