FRACTION NO. 1 VEINS. 



145 



the cross section (fig. 39), which is transverse both to the vein and to the faults. 

 .This crass section is taken along the series of inclined workings on the vein, 

 which run from a point about 60 feet above the upper level to below the lower 

 level. The portions actually exposed are indicated by solid lines, the intervening 

 portions are dotted. It will be seen that the vein follows a series of pronounced 

 rolls, steepening and flattening alternately. In the mine it is evident that these 

 rolls are the result of pressure and deformation in the rock, and are in the 

 nature of folds. On the two upper levels, at the sharp bend or apex of these 

 folds, as shown in the cross section, tangential fractures or slight faults leave the 



Scale 



30 



mofeet 



300-rt./evel 



400-ft./e*el 



FIG. 39. Cross section of Fraction No. 1 vein, along drifts and winzes. 



vein and pass off into the surrounding andesite. Some of these become horizontal, 

 some nearly vertical, and both strike nearly parallel with the vein. Between the 

 300- and the 400-foot levels, a flat fault, striking and dipping in the same way as the 

 vein, has probabty the same origin as the flat tangential slips in the upper levels, 

 but is here of greater magnitude, so that the vein has actually been faulted con- 

 siderably along it. The incline from the 300- to the 400-foot level follows this 

 fault for some distance after the disappearance of the vein. The fault which 

 terminates the vein at its lower end in the cross section belongs to the northeast 

 system, and Is thus different from any other of the faults shown in the figure. 

 16843 No. 4205 10 



