DOMAIN I. SIDEROUS. 



there observed any crater from which they could 

 have issued, nor distinct currents by which they 

 might be traced to their origin. It might be 

 thought that they consist of melted granite, 

 wrought and ejected by volcanic agents. The 

 homogenity of their paste shows how complete 

 the fusion or igneous dissolution has been, and 

 scarcely permits one to believe that the number 

 of crystals of felspar which they contain, should 

 have pre-existed the fusion, and withstood it. 

 The form of these crystals, their laminar struc- 

 ture perfectly preserved, their transparency, 

 their facility of melting, their manner of being 

 in these vast masses, and in short their analogy 

 of composition with the paste which surrounds 

 them, leads one to believe that they were formed 

 during their igneous fluidity, by an approxi- 

 mation of their integrant parts, which were able 

 to obey the laws of their affinity. These por- 

 phyroids are the most ancient of all the volcanic 

 productions of Auvergne : they are covered with 

 basalt, and contain veins of -that substance. 



" However different these productions may 

 be, however distant the various periods of their 

 formation, they do not seem the less united in a 

 certain degree, and form, in some sort, an identic 

 system. Cantal, Mont Dor, Puy de Dome, &c. 

 the most ancient of the volcanic masses, are in 



