STRUCTUEAL RESULTS OF FAULTING. 



179 



the hanging wall might not unlikely form at greater depths as well, but 

 would partly close again, leaving behind only openings of limited size, 

 because the pressure and motion of the superincumbent mass would suffice 

 to grind to powder most of the intervening fragments. 



Relation of chimneys to surface topography. If in faulting, the rislug COUUtry slliftS 



in the direction of the strike of the fissure, of course chimneys will form 

 where the strike undulates. Where the surface is modified by faulting in the 

 manner discussed, such chimneys will always lie on the same side of ravines 

 on the surface, and opposite them will be found crushed ground arising 

 from the pressure of the walls upon one another. 



Infrequency of a rise of the hanging wall. ThrOUghoUt tho forCgoiug disCUSSloU I 



have supposed that the relative movement of the foot wall of the fissure was 

 upward, according to the well-known empirical rule. Were the reverse 

 case to occur, the resulting curve would still be a logarithmic one, but 

 would be constructed in the acute angle between the fault line and the 

 asymptote parallel to the original surface, 

 and uidess faulting has gone on but to a very 

 slight extent, or unless the fault line dips at 

 very close to !)0°, the resulting surface will 

 not merely be precipitous, but form a reen- 

 trant curve, and the upper country will over- 

 hang the lower (Fig. 11). Countless faults 

 have been formed in past geological eras, 

 the surface indications of which have been 

 utterly obliterated, but thei-e must be a very 

 great number which still exhibit their features 

 in a recognizable form ; and if it were a usual thing for the hanging wall 

 to rise, overhanging surface would not form one of the rarest of topograph- 

 ical phenomena. 



Applications of the theory to the Comstock, and other instances. — The evi- 

 dences, already alluded to, of the division of the east and west country 

 of the Comstock L'-de into parallel sheets lend probability to the suppo- 

 sition that the faulted structure of the central poi-tion of the vein may 



(jf tlie hau^iui; wall. 



