1922] Whitman: Genesis of the Ores of the Cobalt District 267 



ated and oriented not with reference to local structures, but rather 

 to the major stresses. Jointing of this type is more abundant and 

 more perfectly developed near the surface, and is to be regarded as a 

 strictly surface phenomenon. Further notice of the uncemented joints 

 is unnecessary beyond the observation that in general they grow less 

 abundant and less perfectly developed with depth. 



Fig. 3. Showing relation of vein content to dip of veins. 



Cobalt-Silver Veins 



The veins logically fall into the following types, which are 

 arranged in the order of their productiveness: (1) The first or normal 

 type includes only veins formed in split joints. (2) The second in- 

 cludes veins formed in major joints branching from or parallel to 

 steep faults. (3) The third includes veins formed in faults. (4) The 

 fourth includes veins formed in shear joints and faults of low dip. 



Vein contents. — Calcite and dolomite are the characteristic gangue 

 minerals, the latter being usually more intimately associated with the 

 ores. The other constituents are grouped in the veins more or less 

 together, and occur in accordance with definite rules, very interesting 

 and significant relations being discoverable in them. The rules are 

 for the most part well represented by the accompanying diagram 4 

 (fig. 3), in which the richness of veins is shown to be proportional 

 to their angle of dip. 



4 After W. L. Whitehead, Eeon. Geol., vol. 15, no. 2, p. 117. 



