Continuity of Metalliferous depositories in Depth. 353 



the dimensions in two senses. Besides this, the fractures 

 have experienced a certain difficulty in extending their direc- 

 tion, because the formations are possessed of a greater or 

 less degree of flexibility ; but the causes of these fractures 

 being subterranean, they must have admitted of a much 

 easier propagation in regard to depth. The further we de- 

 scend in veins, the nearer we come to the seat of the action 

 which has determined their formation. 



Veins of 500 metres of continuity or length are small veins, 

 and we can refer to a much greater number, which exceed 

 1000 metres. The veins of Freiberg afford frequent ex- 

 amples of 4000 meti-es of ascertained length ; those of the 

 Hartz from 4000 to 8000 metres ; 6000 metres at least are 

 assigned to Holzappel ; lastly, some veins attain to a length 

 of 12,000 metres and upwards. 



Let us see how our theoretical hypothesis of a greater 

 continuity in depth applies in those mines where the works 

 are most extensive. The Samson vein at Andreasberg has 

 been traced only for a length of 700 metres ; now this vein 

 is at present excavated to the depth of 800 metres, and no 

 alteration in its allure indicates any approach to a termi- 

 nation. 



Here then is an example of a vein vv^hose continuity, ac- 

 cording to the inclination, greatly exceeds the continuity in 

 direction. But the Samson vein is only a fissure in the 

 ground, of 0™-60 mean deviation. If this small fissure pre- 

 sent such marks of continuity, what notion may we form 

 respecting the continuity in depth of the Hartz veins, which 

 are 10 metres of medium vs^idth, and 8000 metres in length. 

 The neighbourhood of Andreasberg aff'ords us many instances 

 of veins explored to depths nearly as great as their continuity 

 in direction or length ; there are othei's at Joachimthal ; 

 others in Cornwall, where the mines of Dolcoath, for ex- 

 ample, have been followed to 600 metres of veins which 

 presented no variation of allure, although their dii-ection 

 or length was only from 800 to 1000 metres. 



But fewer objections ai'e made to the continuity of the 

 fractures tiian to that of the minei'als. Let us examine this 

 second point. 



