54 G. F. BECKER — STRUCTURE OF THE SIERRA NEVADA. 



was divided into smaller fragments by the fissure systems and sometimes be- 

 cause its position exposed it in a greater degree to the action of the ice. 



So infrequent are large faults that I soon came to suspect the character of 

 any dislocation apparently exceeding a few inches, and in most cases I found 

 that such appearances were referable to merely superficial action. 



The horizontal movements on the fissures are of the same order as the 

 vertical movements and I am unable to state from observation which on the 

 average is the greater. Very often the exposures are such as to render only 

 one of the movements determinable, and it appears that, just as the amount 

 of vertical faulting on parallel fissures is variable, so too is the ratio between 

 the vertical and the horizontal motions. In many cases, however, it can be 

 shown that the two movements were not very different. 



Rules of Faults. — Throughout the area here treated I have found not a 

 single exception to the following rules of the faults on the two vertical fissure 

 systems which strike respectively north-north w^est to south-southeast and east- 

 northeast to w^est-southwest, where the surface had undergone no superficial 

 dislocation: 1, the northerly wall has moved upwards and westwards 

 relatively to the southerly wall ; 2, the easterly wall has moved upwards and 

 southwards relatively to the westerly wall. These rules maintain their 

 validity even when an exception might be looked for. The fissures which I 

 call vertical are of course not absolutely so, for that would be impossible. 

 Often they are so nearly vertical that the eye detects no deviation from a 

 plumb line suspended in line with them ; but sometimes there is a divergence 

 of a few degrees in one direction or the other. One might then expect that 

 the hade would alw^ays be to downthrow, but this familiar movement has 

 taken place only when it was compatible wath the rules just stated, and in 

 other cases the hade is to the upthrow. I have been astonished to meet no 

 exceptions to these rules. 1 should have supposed that variations in density, 

 preexisting fissures, and the like, would necessarily have induced local ex- 

 ceptions to any general rule. It may be that there are such exceptions, but 

 I certainly failed to find any. To the north of the area here examined, in 

 the neighborhood of Mt. Lola, there is another set of vertical fissures inter- 

 secting those for which the rules were given at angles of about 45°. The 

 dislocations are there so complex that I did not succeed in systemizing them, 

 and they may be found exceptional. 



Inductive Examination of Dislocating Forces. 



RELATIONS OF THE MOVEMENTS. 



The various disturbances are so associated as to indicate that they took 

 place simultaneously, and their uniformly systematic character over a large 

 area suggests that they must have been due to some set of parallel forces 

 pretty uniformly distributed with reference to the mountain mass. I shall 



