356 M. Mohs on the Discovery of Useful Minerals. 



in respect to a whole series of rocky masses, is applicable to 

 each individual portion, if we have sufficiently ascertained the 

 relations of that portion to the whole. Without this know- 

 ledge we are deprived of a great part of the guidance which 

 in such operations may render valuable assistance ; and hence 

 we would do well to exceed the prescribed limits on all sides 

 as far as necessary to assure us that we have perfectly com- 

 prehended the most general, and therefore the most important 

 phenomena. As this requires no special notice after what has 

 been already said, it only remains for me to speak shortly of 

 the procedure necessary with respect to the object under con- 

 sideration in the secondary roclis. 



The constitution of the rocks termed secondary in plains, 

 is much simpler than that of the mountain-masses in the dis- 

 tricts which l)ave been already discussed ; and hence also the 

 mode to be followed in searching for valuable repositories of 

 useful minerals is also more simple ; and of these we have 

 only to consider those occurring in beds, as veins are to be 

 treated in the maimer just described. 



'::i The first thing to bo done, in reference to a bed-like mass 

 which has been found, is to ascertain that nothing more is to 

 be sought for in or under it. If wo are acquainted with its 

 extent and breadth, we can not only limit more narrowly the 

 district in which we are to pi-osecute our researches, but can 

 also obtain an idea of its form and constitution, for the vari 

 Qus rocky masses occurring in such a district are generally 

 uniformly stratified in respect to one another. Hence, if we 

 have found the outgoing of a bed of useful minerals, or if we 

 have grounds for supposing the presence of such a bed, we 

 are already in possession of sufficient information to guide us 

 in its further exposure. The different cases A\hich can occm* 

 may be referred to the two following. The various rocky 

 masses either so repose on one anotlier that their strike for 

 great distances is a straight line, and their dip everywhere 

 towards one and the same point of the compass, and that un- 

 der neai'ly the same angle ; or their strilve changes its direc- 

 tion as well also as the dip, and in such a manner that the whole 

 rocky mass is inclined on several or on all sides towards a 

 certain line, or a certain point in the interior, or. to express 



