GEOLOGY. 159 



which the people attribute a singular origin ; the 

 traveller will take fragments of them, some may be 

 aerolites, others may have been transported by the 

 revolutions of the globe. 



In gathering the fragments of rocks, mines, vol- 

 canic productions, fossil organised bodies, the most 

 essential thing is to notice their bearing, that is to 

 say, the nature of the soil where they are found, 

 and their position relative to the minerals which 

 environ them. 



The basaltic layers merit a particular attention, 

 either in themselves, or with respect to the soils 

 which support or which cover them ; the traveller 

 will remark if they are divided into irregular 

 masses, in tables, prisms, and what is their disposi- 

 tion. He will observe if they contain the remains 

 of organised bodies, and he will take care to collect 

 specimens of the different states, as well as of the 

 substances upon which the basalt reposes. He 

 will particularly ascertain if there be not any inter- 

 position of scorified matter, or of those beds of an 

 earthy aspect, to which the Germans give the name 

 of wakke, and which are not supposed to be vol- 

 canic. 



The trap porphyries or trachytes, merit the same 

 attention : they are particularly distinguished from 

 primitive and transitive porphyries, by the ab- 

 sence of quartz and the presence of pyroxene. 



The traveller will not trouble himself with 



