84 DOMAIN I. SIJDEROUS. 



" This cement is more than semi-hard, it easily 

 gives sparks under steel, and may nevertheless be 

 scratched by a knife, the streak being of a rose 

 colour. It melts with difficulty under the blow- 

 pipe into a semi-transparent glass, grey and full 

 of bubbles, mixed with some brown dots, which 

 are attractable by the magnet. 



" The grains are of felspar, white, yellowish, 

 rarely crystallised with regularity, and of the unc- 

 tuous nature of the preceding. 



1539- D. " Black porphyry. The paste of this 

 is of a fine deep black, approaching a little to 

 blue : its exterior surface is pretty uniform, and 

 almost soft to the touch. Its fracture delicately 

 scaly, as that of the preceding ; but its hardness 

 rather less, although it yields some sparks. It is 

 still more refractory ; the flame of the blow-pipe only 

 whitens and blunts it a little on the thinnest edges. 



" The grains, of a greenish white, have no regu- 

 larity ; they are cemented in the black base of the 

 stone, in all sorts of forms. Their fracture is 

 most frequently scaly: there are however to be 

 seen some marks of the laminar texture of the 

 felspar, and it is also, as in the others, of the unc- 

 tuous kind. 



1539- E. " Brown porphyry. Its cement is 

 brown, rough, and of an earthy aspect ; it is how- 

 ever pretty hard. The grains, seldom regular, are 



