408 FUALTS INTERSECT METALLIC VEINS. 



bable that most of the Springs, that issue from unstratified 

 rocks, are kept in action through the instrumentaUty of the 

 Faults by which they are intersected. 



A similar interruption of continuity in the masses of Pri- 

 mary rocks, and in the rocks of intermediate age between 

 these and the Coal formation, is found to occur extensively 

 in the working of metallic veins. A vein is often cut off 

 suddenly by a Fault, or fracture, crossing it transversely, 

 and its once continuous portions are thrown to a considera- 

 ble distance from each other. This line of fracture is usually 

 marked by a wall of clay, formed probably by the abrasion 

 of the rocks whose adjacent portions have been thus dislo- 

 cated. Such faults are known in the mines of Cornwall by 

 the term Jlucan, and they often produce a similar advantage 

 to those that traverse the Coal measures, in guarding the 

 miner from inundation, by a series of natural dams travers- 

 ing the rock in various directions, and intercepting all com- 

 munication between that mass in which he is conducting his 

 operations, and the adjacent masses on the other side of the 

 flucan or dam.* 



It may be added also that the Faults in a Coal field, by 

 interrupting the continuity of the beds of coal, and causing 

 their truncated edges to abut against those of the unin- 

 flammable strata of shale or grit, afford a preservative 

 against the ravages of accidental Fire beyond the area of 

 that sheet in which it may take its beginning ; but for such 



* " My object is rather to suggest whether the arrangement of veins, &c. 

 does not argue design and a probable connexion with other phenomena of 

 our Globe. 



" Metalliferous veins, and those of quartz, &;c. appear to be channels for 

 the circulation of the subterraneous water and vapour ; and the innumera- 

 ble clay veins, or ' flucan courses ' (as they arc termed in Cornwall,) which 

 intersect them, and are often found contained in them, being generally im- 

 pervious to water, prevent their draining the surface of the higher grounds 

 as they otherwise would, and also facilitate the working of mines to a much 

 greater depth than would be practicable without them." — R. W. Fox on the 

 Mines of Cornwall, Phil. Trans. 1830, p. 404. 



