M. Mohs OH the Discovery of Useful Minerals. 336 



nences ; and in doing this the following' particulars are to be 

 carefully noted: First, the height above the sea, which is to be 

 determined barometrically ; and also the height above the foot 

 of the mountain, and above those points of the valleys run- 

 ning towards the eminences, at which they begin to ascend 

 more or less rapidly. The points at which the measurements 

 are made, must of course, be accurately entered on the map. 

 Secondly, the mountain-rocks must be fully examined, their 

 nature must be determined, and well-selected specimens col- 

 lected. The direction and dip of the structure-surfaces, or 

 in other words what is termed the stratification in slaty moun- 

 tain masses, must be determined at as many points as pos- 

 sible ; all considerable changes in direction and dip must be 

 indicated on the map ; and even the smaller bendings must 

 not be left unnoticed. Farther, the alternation of the moun- 

 tain masses, when such occurs, must be observed, and also 

 the appearances these masses present at their junction, in re- 

 spect to the changes which the particular rocks themselves, 

 or the mountain-masses, undergo under such circumstances ; 

 the passages that occur, and the foreign substances which se- 

 parate two masses of rock from each other at their junction 

 must be minutely examined ; and finally, it is necessary to at- 

 tend to the minerals which do not enter into the composition 

 of the mountain-rocks themselves, such as garnet, tourmaline, 

 &c., but which occur in one or the other of the neighbouring 

 masses, either near or at least at no great distance from their 

 common junction. All such observations, however unimport- 

 ant they seem, may, when combined with others, eventually 

 become of moment, and may, at all events, sex-ve or contribute 

 to enable us to recognise the mountain-masses that have been 

 examined in more remote places, an assistance which is at- 

 tended with much advantage in our researches. Thirdly, 

 We ought from these high points to endeavour to obtain as 

 connected a general view as possible of the surrounding dis- 

 tricts, which gradually may produce a representation of the 

 whole mountains, that will be at least much more lively, and 

 much more calculated to enable us to draAV conclusions, than 

 any which could be obtained directly from the map. The 

 features of the principal chain, and of the lateral chains, tl»e 



