336 M. Mohs an the Discovery of Useful Minerals. 



position of the points in these which are most remarkable, 

 either from their height, their external form, or constitution : 

 and also the situation of the valleys and ravines, together w^ith 

 their connection Avith one another, are important objects of 

 attention. Opportunities will not be awanting of perfecting 

 the map, either by adding phenomena worthy of observation, 

 which the small scale of the original did not allow of being 

 represented, or by endeavouring to correct, as far as is per- 

 mitted by the circumstances, or is necessary for our object, 

 little errors which are almost unavoidable in representations 

 of this kind, and which can only be noticed by the geologist. 

 It appears advisable to bring into connection what has now 

 been pointed out, and completely to finish it before beginning 

 the actual search for deposits worthy 'of being excavated by 

 mining operations. In this manner, while, on the one hand, 

 we obtain the most accurate and best preparatory introduc- 

 tion to this search ; on the other hand, during that search, we 

 are not disturbed or distracted by such observations, for ex- 

 ample, by barometrical measm'ements, and are therefore not 

 necessitated to carry fragile instruments every where with us, 

 which might perhaps prevent us from ascending rocks or fol- 

 lowing paths where personal safety would require all our atten- 

 tion, and where we might not be able to bestow attention on 

 other things besides the hammer. It must here be remarked, 

 then, when we find an opportunity of making observations of 

 any kind on our road to the above-mentioned high points, in the 

 valleys, or on the acclivities of the ridges, we should take ad- 

 vantage of them even when we know previously that we are 

 again to pass over the same ground ; for in investigations, 

 which, when they are successful and are not dependent on 

 accident, ai*e combined with so many difficulties as the dis- 

 covery of repositoi'ies of useful minerals that would repay 

 the expense of mining operations, we ought to pass over no- 

 thing which tends to advance them, and to diminish the ar- 

 duous nature of the undertaking ; and this is done by every 

 accurate observation. 



After we are in possession of this general view, we are pre- 

 pared to sketch out a proper plan for the actual investigation 

 in aid of the disco veiy of repositories of useful minerals. Such 



