CLASSIFICATION OF ORE DEPOSITS. 55 



5. Occupying collapsed (brecciated) beds, 



caused by solution and removal of sup- 

 port, or from dolomitization of limestone. 

 (Southwest Missouri zinc deposits. 1 ) 



6. Occupying cracks at Monoclinal bends, 



Anticlinal summits, Synclinal troughs, 

 often with replacement of walls. (Gash 

 veins in part ; galena deposits at Mine 

 la Motte, Missouri ; zincblende deposits 

 in the Saucon Valley, Pennsylvania. 3 



7. Occupying Shear-zones, or dynamically 



crushed strips along faults, whose dis- 

 placement may be slight, closely re- 

 lated to No. 8. (Butte, Mont.*) 



8. True veins filling an extended fissure, often 



with lateral enlargements. See also un- 

 der 5. 



9. Occupying Volcanic necks, in agglom- 



erates. (Bassick and Bull Domingo 

 Mines, near Rosita, Colo. 5 ) 



10. Contact deposits. Igneous rocks almost al- 



ways form one wall. Fumaroles. (Mar- 

 quette hematites, Michigan. 6 Greisen.) 



11. Segregations formed in the alteration of 

 igneous rock. (Chromite in serpentine.) 



III. Deposited from Suspension. 



1. Metalliferous Sands and Gravels, whether 



now on the surface (placers, magnetite 

 beach-sands), or subsequently buried. 

 (Deep gravels, magnetite lenses ?) 



2. Residual Concentrations, left by the 



weathering of the matrix. (Iron Moun- 

 tain, Mo., hematite in part. 7 ) 



1 F. L. Clerc, Lead arfd-Zirtc-Ores in Southwest Missouri Mines, 

 Carthage, Mo., 1887; A. Schmidt, Missouri Geol. Survey, 1874, p. 384. 



2 T. C. Chamberlain, Wis. Geol. Survey, IV., 1882, 367. 



8 F. L. Clerc, Mineral Resources, 1882, p. 361; H. S. Drinker, Trans. 

 Amer. Inst. Min. Eng., I. 367. 



4 S. F. Emmons, Trans. Amer. Inst. Min. Eng., XVI. 49; W. P. Blake, 

 idem, XVI. 65. 



6 C. W. Cross, Proc. Colo. Sci. Soc., 1890, p. 269. 



6 C. R. Van Hise, Amer. Jour. Sci , February, 1892, p. 116. 



7 R. Pumpelly, Bull. Geol. Soc. Amer., II., p. 220. 



