M. Mohs on the Discovery of Useful Minerals. 347 



various rocks, &e. {i-dumlichen verhdltnisse). We must care- 

 fully avoid going beyond vs^hat has been directly observed, 

 and must therefore insert nothing which does not result from 

 personal observation ; for it is in this way alone that we can 

 be made aware of what we have still to learn. When we 

 combine remote points of observation by lines, without refer- 

 ence to the points lying between, erroneous views may be 

 formed, which Ave ought to be on no occasion more anxious 

 to avoid than in an occupation of this kind, where errors are, 

 in the very nature of the case, so easily possible, and at the 

 same time so productive of evil. 



But when we have, with proper care, delineated on the map 

 the observations which have been collected, we can then judge 

 of the identity of the mountain-masses in the various valleys 

 that have been examined, and of the beds M'hich are distin- 

 guished by a different mineral constitution, and we can then 

 obtain a complete knowledge of their extent and distribution. 

 If we find that a mountain-mass, or a bed, does not make its 

 appearance where, in the regular course, it might be expected, 

 we must examine the causes, and we shall find them to con- 

 sist in this, that the mountain-mass has become altered in the 

 nature of the rock of which it is composed, or that it has 

 wedged out. The one phenomenon is as important as the 

 other ; for with the alteration of the rock there are often on 

 the surface of contact new phenomena, which may be advan- 

 tageous or the contrary, but which must be, in either case, as- 

 certained ; and at the wedging out, other mountain masses 

 come in contact with one another ; and what farther takes 

 place must be determined by direct observations, and must 

 ijot be assumed from probabilities or suppositions. If another 

 mountain-mass has presented itself, then all kinds of special 

 o'ccurrences come into consideration, and must be judged of and 

 treated as has been previously described. If a mountain-range 

 should possess a very considerable breadth, it is necessary, 

 even though none of the circumstances just detailed exist, to 

 examine it more closely, if we have not already made ourselves 

 sufficiently accpiainted with the range by means of the lateral 

 valleys and I'avincs, in order that we may acquire as many 

 tlata as possible for ascertaining perfectly the constitution of 



