CHEMICAL REACTIONS IN THE GRAVELS. 



331 



which they occur. Were this not the case, the lodes would be so faulted 

 and disturbed the working them would be almost or quite an impossibility. 



i 



Faulting of the lodes, however, even in a slight degree, is not common, and 

 the existence of any very extensive breaks is something unknown to the 

 writer; such must, at all events, be of rare occurrence. There is also abun- 

 dant evidence that the volcanic epoch was not inaugurated in the Sierra 

 until the range had approximately its present form. This, however, must 

 not be taken as excluding the possibility of the presence of eruptive masses 

 in the bed-rock itself. These do exist, and probably in great quantity, al- 

 though in a much metamorphosed condition, so that it is not easy to recog- 

 nize their real nature, except by the aid of the microscope. But the era of 

 volcanic action belonging to the bed-rock series is widely separated from 

 that of the gravel formation, as shown by abundant facts : the one seems to 

 have been the result of massive eruptions ; the other was undoubtedly that 

 of the ordinary crater ejections of the present day. 



We have, then, the two sets of phenomena — the formation of the quartz 

 veins in the bed-rock, and the covering of the gravel deposits with eruptive 

 materials — brought very near each other in geological time. That these 

 occurrences were absolutely synchronous cannot, of course, be maintained, 

 because we have rolled fragments of quartz under the lava in many places, 

 showing that veins or masses of this material existed before the opening of 

 the volcanic epoch. The epoch of metamorphism proper seems to have 

 been the first stage in the process which was to culminate in the pouring 

 forth from the crest of the Sierra of the immense mnss of eruptive material 

 which now rests upon its flanks. That during or soon after the meta- 

 morphism of the slates the quartz veins began to be developed, is also a 

 reasonable supposition, and we know that these phenomena were followed by 

 the opening of a line of orifices from one end of the range to the other, 



matter in its various forms, as 

 already indicated. That these various stages of chemical action are geneti- 

 cally connected cannot, in the present state of our knowledge of the myste- 

 ries of volcanic activity, be positively affirmed ; but certainly the evidence 

 pointing in that direction is wvy strong. 



It might appear that what has been said above, in regard to the formation 

 of the quartz veins after the range of the Sierra had assumed its present 

 development, was in contradiction to what had been previously stated m this 

 volume in reference to the peculiar form of the "Great Quartz Vein," as 



through which vents came the eruptive 





