4$ BOMAlN I. SIDEROUS, 



numerous are currents of lava, which lead to 

 craters still existing; the second are masses or 

 tables of basalt, separated by rifts or valleys ^ 

 the third consists of mountains whose mass is a 

 kind of volcanic porphyry. 



"1st. Lava in form of currents. There are in 

 Auvergne near a hundred conical, isolated moun- 

 tains, from 200 to 400 yards in height, formed 

 of heaps of scoriae, fragments of lava and of la- 

 pillo : their summit often presents a hollow in 

 the form of a cup or crater : they rest imme- 

 diately on granite. From the bottom of several 

 of them currents are observed to run of lava of a 

 basaltic nature, that is of a greyish black, with 

 a fine compact grain : this lava contains grains 

 and crystals of peridot (olivine), augite, felspar, 

 &c. The superficies is blistered and studded 

 with asperities, which sometimes attain and even 

 surpass a yard in height: the interior is more 

 compact, and less porous, as you arrive nearer 

 to the bottom. The currents are spread in the 

 adjacent plain ; they have sometimes reached 

 the bottom of certain valleys, and have followed 

 their Bourse for a distance of three or four 

 leagues ; in advancing progressively they always 

 incline to points lower and lower ; they follow 

 the inequalities of the soil; they separate, on 

 meeting with any obstructing eminences in their 



