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 M. Mohs on the Discovery of Useful Minerals. "353 



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size, it is advisable to become acquainted with its proportions, 



that is, its extent in different directions ; for, on these, other cir- 

 cumstances being equal, depends the Aalue of the discovery. 

 Local circumstances will indicate how this can best be done. In 

 every case, however, the vicinity of such a repository must be 

 well examined ; and, as this cannot be accomplished in the 

 same manner as in the case of a bed, a few remarks on the 

 subject may not be unnecessary. If the mountain-mass which 

 includes the irregularly-shaped repository has not a slaty struc- 

 ture, and exhibits no tabular concretions ( plattenformige zu- 

 sammense/zunffj, as is in some instances the case in limestone, 

 we can only take the general relations of stratification as a 

 guide to lead us to others, when we are informed of the pre- 

 sence of such repositories by our having already discovered 

 one of them. We therefore examine the mountain-mass by 

 means of its natural, or, when necessary, by artificial exposures, 

 we attend particularly to fragments, &c., and extend this inves- 

 tigation to a sufficient extent, as it is generally a whole region 

 or a mass of large dimensions in the mountains in which such 

 .irregularly-shaped repositories occur, so that from the discovery 

 of one we may anticipate the existence of several. If the rock 

 possesses a slaty structure, or if it presents tabular concretions, 

 we must observe cai*efully the relation of the repository to the 

 structure. For if the direction of the structure is cut by the re- 

 pository, and not altered by its presence ; further, if transitions 

 present themselves from the mass of the mineral or of the repo- 

 sitory into the mountain-mass, little else can be done but what 

 has been already pointed out ; but if the direction is so altered 

 that the tabular concretions on the lai-ge scale exhibit bond- 

 ings, and the smaller structure, or that of the rock, as it were 

 clings to the mass of the repository, the latter will probably 

 become contracted at the opposite end, and perhaps, after 

 having lost its size, a trace may still be perceived on the sur- 

 face of the distinct concretions, Avhich will serve as a guide ; 

 and though this should not be the ease, yet we can become 

 acquainted with the tabular masses between which the repo- 

 sitory is contained, and can follow them up. But, when we 

 have lost all traces, we must more particularly notice the 

 bendings which may probably present themselves in the struc- 



