358 M. Mohs on the Discovery of Useful Minerals. 



point, we make the fii'st bore do^\^l to the fundamental rock. 

 This fundamental rock must be reached with certainty, and, 

 in order to be fully assured of it, it may be proper to pierce 

 it for a few feet. The rocky mass in which the first bore has 

 been made, if it has been penetrated throughout its whole 

 thickness, will be considered as the fundamental rock in further 

 trials, but only in so far, that, when the first bore is made in 

 another and a superimposed mass, it must be again reached 

 by it, and not with the understanding that in it (in some de- 

 gi'ee in another series) nothing more is to be expected or 

 sought for. If this rocky mass superimposed on the subjacent 

 one, or any other of the rocky masses under investigation, be 

 so extensive, or its dip so considerable, that it cannot be com-: 

 pletely traversed by one bore ; we then divide it according to 

 its levels and the general relations of its stratification, into 

 several parts, and treat each of these subdivisions as an in- 

 dependent one distinct in its rock and different from the 

 rest of the rocky mass. But, as the surfaces of superposi- 

 tion generally, or the actual clefts of stratification which 

 exist, are not perfect plain surfaces, and as all kinds of bend- 

 ings occur and may cause ei'rors in the result ; in order that 

 we may proceed quite safely, we ought rather to do too much 

 than too little, and make the bores pass one another for a 

 distance of some feet or fathoms. We thus carry on our 

 labour in so many parallel series of bores, and in so many 

 separate bores in these series as we think necessary, until 

 we reach the rocky mass which forms the general covering 

 of all the others, or regarding which we know that nothing 

 more is to be found in or over it, and can feel convinced 

 that, if Ave pierce this superimposed mass likewise and find 

 nothing, then the whole examined series of strata can con- 

 tain no repositories of useful minerals. This is the general 

 mode of procedure which, according to pai'ticular circum- 

 stances, may be modified, and not unfrequently greatly cur- 

 tailed. 



We have presupposed repositories which extend over the 

 whole system of stratification. How we are to vary opera- 

 tions with less extended repositories, is of itself evident. It 

 is requisite in such cases to carry the bores which we have 



