360 M. Mohs on the Discovery of Useful Mi7ieralis. 



to their structure and other relations, gives no indication as 

 to where it is to be found, we must seek to discover it by 

 openings made down to the solid rock ; the direction of which 

 openings ought to be perpendicular to the direction of the 

 structure of the mountain-masses or of the rock structure, 

 or, where that cannot be recognised, to the known direc- 

 tion of the strike of the repository or bed. We take the 

 portion thus ascertained as a new starting point, and again 

 continue to prosecute_our operations a before. If, notwith- 

 standing all the means employed, the repository of useful 

 minerals should not be discovered at any such point, and 

 indeed no trace of it detected, we must not rest satisfied, 

 and far less abandon the whole search ; but we must I'eturu 

 to the last known point, and from it endeavour to meet with 

 it at a shorter distance off, perhaps about half-way between 

 the two. Whether Ave should find it here or not, we shall at 

 least be guided as to how we are further to proceed. The 

 object of this exammation is to ascertain the way and man- 

 ner in which the repository loses itself ; that is, if it wedges en- 

 tirely out between the I'oof and floor, or if it, as it were, dis- 

 appears in the rock by its component parts entering into the 

 mass, being collected in it, and these at last passing into the mere 

 rock, or if it is altered from its original position, or entirely 

 cut off by displacement. We can from these circumstances, 

 in some degree, form an opinion of what is to be expected 

 from the continuation of the repository ; and the last case is 

 the one which promises least, though likewise there is but 

 little to hope when the repository changes its natm'e, and is, as 

 it were, changed into the mountain-mass. Still, we must not 

 entirely depend on such being tlie case, but must anew investi- 

 gate 4he repository where the nature of the surface, and the 

 exposure of the rocks, permit ; and, with the assistance of the 

 information acquired of the relations of the stratification, and 

 the nature of the rock, this has no particular difficulties, so 

 soon as we are assured, in a general way, of the existence of 

 such a repository, and are acquainted in some degree with the 

 circumstances under which it presents itself ; and it is only 

 when it is not to be found at any of the points, and when no 

 other trace of it can be discovered, that we can assume that it 

 has entirely ceased in this direction, and terminate the inves- 



