362 ON THE APPARENT DISLOCATIONS [Ch. XV. 



supposed fissures, would immediately fall to the bottom of the 

 empty chasm, or subside through the injected fluid, whether 

 igneous or aqueous, and not remain in positions which com- 

 monly correspond with the bearings of the adjoining mass. 

 And let it be also remembered, that these insulated portions 

 also abound in veins of various sizes, sometimes composed 

 entirely of metallic minerals, and at others of quartz ; at one 

 time intersecting likewise the matrix of the large vein, and 

 at another being blended therewith ; and, moreover, these 

 subordinate lodes (or veins within veins) exhibit all the phe- 

 nomena of true veins, not even excepting those commonly 

 referred to movements. How and when were such veins 

 formed ? When they occur in granite, they are called con- 

 temporaneous. According to the prevailing theory, however, 

 this cannot be their origin, because the fragments of rocks, 

 and the matrix of the vein, cannot be supposed to be of the 

 same formation. How then could the different series of inter- 

 secting subordinate veins be produced? How could the 

 successive fissures and injections be accomplished within the 

 consolidated vein? These objections equally apply to all 

 veins in rocks, which are known to terminate in length and 

 depth, as indeed they would also to true veins, if we would 

 only admit the analogy of the known to apply to the unknown 

 limits, instead of concluding that the largest veins must be 

 of indefinite depth, because they extend lower than 1 500 feet 

 below the surface ; a measurement utterly insignificant com- 

 pared with the probable thickness of the earth's crust, and 

 therefore not an adequate datum for such a deduction. 

 Analogy is surely, in this case, the safer guide of the two. 

 We find veins descend to a certain depth, retaining their 

 average breadth till they terminate ; others continue their 

 course lower than the deepest mines, but they likewise may 

 not extend beyond limits, which may be of moderate dimen- 

 sions compared with the diameter of the globe, though pro- 

 bably extending beyond the reach of mining operations. 

 It is time, however, to turn our attention to the inter- 



