354 M. Amedee Buriit on the 



Theory rests here only on a single principle : the origin of 

 minerals is owing to subterranean actions. Admitting that 

 the depths to which we can descend by subterranean works 

 are inconsiderable, compared with the distance which exists 

 between the surface and the igneous source of metalliferous 

 emanations, we shall be always led to believe that there is 

 no general reason why the veins should be modified in their 

 mean composition, in proportion as our works become deeper. 

 Let us look at the facts : 



The Clausthal and Zellerfeld group of veins in the Hartz 

 has presented, from the first, concentrations of minerals on 

 the most ramified points of allure. At these points the 

 most productive mines were opened, some of which, such as 

 the Dorothea, the Caroline, &c., were still in high repute at 

 the time of M. Hei'on de Villefosse's administration (1812), 

 and had reached the depth of 400 metres. Since that period 

 they have been deepened to 600 metres, and these same 

 mines have always sustained their pi-oductiveness ; so that it 

 has been admitted that the minerals which, considered in re- 

 gard to their direction, are interrupted by considerable bar- 

 ren zones, have much greater continuity according to the 

 inclination. The actual depth of the mines of Clausthal is 

 640 metres. 



The veins of the circle of Andreasberg, so difi^erent in the 

 conditions of their allure from the veins of Clausthal, aflbrd 

 us a no less striking example of the continuity of minerals 

 in depth. These veins having been explored in 1812 to a 

 maximum depth of 510 metres, the mineral was there found 

 in ribbon-like stripes interrupted in all directions, being from 

 15 to 30 metres at most in continuity. At 660 metres, one of 

 the finest ribbon forms was seen, and the whole of the exca- 

 vations have been deepened to a maximum of 800 metres, 

 without any disturbance in the general conditions of the ap- 

 pearance of the minerals. 



We also find appearances in Saxony not less valuable and 

 instructive than those of the Hartz. The productiveness 

 has there been continued since 1815 by a general deepening 

 of the mines. Eut in the neighbourhood of Freiberg, the 



