DOMAIN I. SIDEKOUS. 



in currents. Thus all the basalts of Auvergnc 

 present proofs, either direct or indirect, of a vol- 

 canic origin; though the degradation of the 

 soil, the dismemberment that the currents have 

 suffered, no longer permit us to retrace the cra- 

 ter from whence they flowed, nor to see the 

 number, form, or extent, of the different cur- 

 rents: the only positive thing we can say in 

 regard to them is, that their existence is anterior 

 to the excavation of the valleys. 



" 3. Porphyroid Masses. The third species 

 of volcanic productions of Auvergne is quite of 

 a peculiar nature ; they are grey stony masses, 

 of a porphyritic structure ; they form eight or 

 ten distinct mountains : the most considerable 

 are Cantal, whose diameter at the base may be 

 about nine or ten leagues, and 900 or 1000 yards 

 high, above its bottom ; the Mont Dor, whose 

 base is five or six leagues, and its height from 

 1000 to 1100 yards; the Puy de Dome, whose 

 base is half a league in diameter, and 600 yards 

 high : the other mountains are still less. The 

 two first are vast masses, torn and irregularly 

 cut by the action of the waters. The substance 

 of which they are all composed is grey, often 

 approaching to black, sometimes to green ; its 

 fracture dull and earthy, with coarser or finer 

 grains j it has little hardness, and easily decom- 



