30 M. Molis" 1 Summary of Geognostical Phenomena. 



of the slate rocks, or, still more, when limestone is in contact 

 with granite, syenite, porphyry, greenstone, without being 

 united by direct transitions, or even when it is separated by 

 traces of a foreign substance, these are circumstances in which 

 there is something to be hoped for, and which therefore ren- 

 der a more close examination advisable. 



Venigenous Stocku-erks. — In the modes of occurrence of useful 

 minerals already considered, the structure of the rock, as well 

 as of the mountain-ma- ses, is generally, though not always, in- 

 tersected ; but there are phenomena where this frequently 

 happens without our being able to say that, by this means, 

 the actual character of the repository is determined ; for 

 there are appearances of this kind, and of perfectly similar 

 nature to one another, which are sometimes conformable to 

 the structure throughout the whole extent, and sometimes 

 are only partially so. These are small, irregular, chiefly ta- 

 bular masses, which, like the so-called contemporaneous veins 

 of calcareous spar in limestone, extend in all possible direc- 

 tions, and, therefore, also in directions parallel to the struc- 

 ture, and which, on account of their insignificance, do not 

 deserve separate consideration. But still there are in cer- 

 tain mountain-masses whole tracts, which, without being con- 

 fined to fixed forms and boundaries, are traversed by simi- 

 lar small veins ; and these are frequently so numerous that 

 they become valuable to the miner, especially since, just as in 

 some of the previously described phenomena, the neighbour- 

 ing rock is frequently metalliferous (impregnated with ore), and 

 hence they undoubtedly become important objects of examina- 

 tion. A part of what are termed Stockiverks likewise belong 

 to the same category ; and tinstone, native gold, and probably 

 some copper-pyrites and glances, are the minerals found in such 

 repositories. We can easily imagine that, towards the boun- 

 daries of such a mountain-mass, traversed by similar veins, 

 these veins appear more subdivided than near the centre ; and 

 hence, when we discover single veins of this kind, we must 

 carefully ascertain if these are not connected with a tract which 

 contains them in a larger number, and of a richer description. 



Like all the other phenomena of nature, this one does not 

 stand alone. In the slate-rocks, in which tho phenomena ai- 



