M. Mohs on the Discovery of Useful Minerals. 357 



it shortly, presents a trough or basm shaped stratification. 

 Under such circumstances, it is not difficult to follow out the 

 outgoing of a mineral repository, when it has been discover- 

 ed ; or to investigate the repository itself, if we have sufficient 

 grounds for knowing of its existence ; and as in this kind of 

 formations the nature of the rock and the phenomena of stra- 

 tification can with peculiar facility admit of our employing 

 the borer, so is this the best means for discovering as well as 

 for examining the value of repositories of useful minerals in 

 the secondary strata. 



If now, we know, in reference to the first of the above-men- 

 tioned cases, those rocky masses in and under which the re- 

 positories sought for are not to be expected, and if we^are 

 fully informed of their strike and dip, we draw at proper dis- 

 tances, of some hundred fathoms, straight lines perpendicular 

 to the strike of their rocky masses, which extend as far as is 

 "necessary from their hanging side in the direction of the dip. 

 This can really be done on the map, but in the field by means of 

 poles. In those lines we take the points at which we mean to 

 proceed v-ath our bore-holes. The distance of these points from 

 the hanging side of the fundamental rock (that namely in and 

 under which our rearches are not to be prosecuted) is deter- 

 mined by the amount of the dip of the rocky masses, and from 

 the nature of the apparatus which we employ ; or also from 

 the knowledge of the general constitution, and extent of the 

 repository regarding which our investigations are carried on. 

 When the dip is inconsiderable, and when we do not avoid 

 making deep bores, the repositories probably possessing con- 

 siderable extent, these distances may be more considerable ; 

 but when the dip is greater, and when, tVom any causes what- 

 ever, the bores are less deep, the repositories being probably 

 of smaller extent, the distances must be less. In the choice 

 of points for the bores, we must take into consideration the 

 nature of the surface, and also other circumstances which can 

 promote or liindei- the operations, and we rather deviate a 

 few fathoms from the above-mentioned line, in order to ob- 

 tain advantages of this kind, or to avoid disadvantages, but 

 only not so far as to irjure or reudei- uncertain the result of 

 the labour. After wc have selcctod a .snitabk- and convenient 



