SUMMAEY. 379 



duced by faulting, and have been only slightly modified by erosion, whence 

 the correspondence of the contours of the foot wall with those of the sur- 

 face. The east fissure is a result of the faulting, and the ore has been de- 

 posited since Washoe became a region of insignificant rainfaH. Tiie sheeted 

 structure of the country is, in all probability, due to the fault. 



It is, of course, most unlikely that the Comstock is the only vein in 

 which the deposition of ore is recent and has been accompanied bv faulting, 

 and a repetition of a part of the conclusions as to the occurrence of veins 

 in such cases may be welcome to some readers. 



Application to other veins. — lu a locality modified by faulting action, attended 

 by horizontal pressure, the fact will appear in the parallelism of the exposed 

 edges and faces of rock sheets. If erosion has not seriously modified the 

 surface I'esulting from the faulting action, the logarithmic curve will be 

 recognizable to the observer looking in the direction of the strike. 



The main cropping of the vein is to be sought at the point of inflec- 

 tion of the curve, which will be found nearly or exactly midway between 

 the top and bottom of the hillside. One or more secondary vein-crop[)ings 

 should be looked for below the main cropping, and these, so far as yield is 

 concerned (but not in regard to location of claim), may prove even more 

 important than the main fissure. 



The dip of the vein will be to the same quarter as the slope of the sur- 

 face, but, of course, greater in amount. The flatter the surface curve the 

 smaller the angle of dip will be. The mean strike will be nearly or quite 

 at right angles to the direction of the spurs and ravines of the faulted area. 



If, besides the movement of one or the other wall in the azimuth of the 

 dip, there has been a dislocation in the direction of the strike, chimneys 

 will open, all of them on the same sides of the difi"erent ravines. Surface 

 evidences will often enable the prospector to determine on which side the 

 chimneys are to be found. On the barren sides evidences of crushing and 

 of closure of the fissures are probable. 



The fissure is more likely to have a constant dip (barring the second- 

 ary offshoots) tlian a constant strike, but, of course, irregularities of dip, 

 like those in strike, will result in chambers which may be productive. 



Offshoots into the hanging wall may occur at any depth, but none, 



