158 MINERALOGY AND 



pass. They will choose the largest, note their size, 

 and break some of these fragments. They will also 

 take some of the smallest, exemplifying the variety 

 of aspect. The further these fragments are brought, 

 the less they become. 



Wherever a rock rises, either in the middle of a 

 water or country, travellers must observe, if this 

 rock be all of the same substance, whether homo- 

 geneous or composite, or if it be formed of different 

 layers. In the first case, they will detach a frag- 

 ment. In the second they will observe the relative 

 position of the strata, their inclination and thick- 

 ness ; they will take a specimen of each, putting the 

 same mark on all the specimens which come from 

 the same mountain, and a particular number on 

 each of them, to indicate the order of their super- 

 position, or their reciprocal situation. If the tra- 

 veller who will collect these specimens, can join a 

 sketch to the simple mention of these particulars, 

 indicating the form of the mountain, and the thick- 

 ness and inclination of these layers, he will perform 

 an essential service. In case the rock be an isolated 

 peak, it will be well to examine and draw two faces, 

 to confirm the inclination of the strata. 



It will be useful to collect the sand of rivers, 

 especially those which carry metallic spangles with 

 them ; but the sand must be taken as far from the 

 mouths as possible. 



In some countries, isolated masses are found, to 



