DOMAIN 11. SILICEOUS. 



on all sides as steep as a wall, and only pierced 

 with a few difficult openings. The summit forms 

 a platform, about 500 paces by 200, covered 

 with blocks and fragments of various kinds of 

 felsite, some laminar, others veined in zigzag. 

 Some have the triangular form of half a cube, 

 cut by its diagonal 5 and one large mass is com- 

 posed of angular fragments of felsite, in a paste 

 of the same substance, so as to constitute a bricia. 



When Dolomieu wrote, the knowledge of 

 rocks was far from having attained even the pre- 

 sent degree of precision ; which is however so 

 far from being perfect, that perhaps another en- 

 lightened century may elapse, before all the 

 rocks shall have been discovered, analysed, and 

 examined, so as to be reduced to their proper 

 domains and modes. The following rock, with 

 a base of his petrosilex, which is felsite, probably 

 belongs to this division, though he mentions it 

 after the toad-stones and variolites*. 



I must here mention some glandular stones 



Corsica. 



which I found in Corsica, chiefly in the valley 

 of Nidof, and which have petrosilex for a basej 

 none have appeared to me more curious nor 

 more instructive. The very fine paste, which 

 forms the ground of the mass, is of different 



* Journ. de Phys. 1794, p. 260, note, 

 t Niolo? 





