356 ON THE APPARENT DISLOCATIONS [Ch. XV. 



After examining this district with Professor Whewell during 

 the summer of 1828, we left it, in the conviction that several 

 of the neighbouring tin works were opened, not upon true 

 lodes, but upon veins of segregation" * These remarks of the 

 Professor were called forth in noticing Mr. Weaver's ob- 

 servations on the metalliferous veins of the south of Ireland : 

 viz. that the copper ore sometimes occurs in true veins ; and, 

 at other times, is very generally diffused either in separate 

 particles, or in strings, veins, and filaments, more or less 

 connected with each other, but not continuous, and therefore 

 contemporaneous with the rocks to which they are subordin- 

 ate. Now this is precisely the condition of both copper and 

 tin ores in Cornwall ; for they are never in that country 

 arranged " in great vertical dykes of metallic ore," as seems 

 to be the common opinion, but in grains and in globular and 

 angular portions of various forms and dimensions, or in layers, 

 veins, and strings, completely insulated either in the quart- 

 zose part of the veins, or in the rocks, whether granite or 

 slate, whether enveloped in angular masses, or horses, in the 

 veins, or connected with the main mass in which the veins 

 are situated. If, then, such a disposition of the ores be an 

 indication of segregation, all the metallic minerals of Cornwall 

 are referrible to this mode of production. And since the 

 metalliferous veins of St. Austle Moor are admitted to have 

 had a similar origin, in what respect do they differ from those 

 in other parts of the county ? Some may say that they are 

 shorter than true veins, and may be generally seen terminat- 

 ing in length and depth : this may appear very plausible, but 

 will not bear the test of a rigid examination. It is true, that 

 innumerable veins in this district answer to this description ; 

 but it is no less true, that, between the smallest of these, and 

 the large regular lodes of the adjoining mines, which have 

 not been outivorked in length or depth, there is a regular 

 gradation as to size : so that no characters have been detected 



* Philos. Mag. or Annals, vol. ix. p. 284. 



