JfOME XI. GRANITE AND GRANITIC PORPHYRY. 181 



phyries. It is not even requisite that the felspar 

 should entirely lose its texture; it is sufficient 

 that it be in vry small plates confusedly inter- 

 mingled, and that it contains other crystals of 

 the same nature, but larger and better marked, 

 and a little distinct by their colour from the base 

 in which they are contained* Thus there is 

 often observed among the Egyptian monuments, 

 at Rome, a rock whose base is a mixture of fel- 

 spar and black hornblende, both in small grains, 

 although still very apparent; in this kind of 

 granitose paste are contained tolerably regular 

 large crystals of white or red felspar, which form 

 spots on the base of the rock, and which give it 

 the greater appearance of a porphyry : as some- 

 times the abundance of hornblende renders the 

 paste which contains these crystals almost en- 

 tirely black*. The granites called the green of 

 Egypt, composed of hornblende and felspar/ 

 become similar to a porphyry, if the proportion 

 of hornblende ever so little exceeds that of the 

 felspar ; because then the crystals of the latter 

 detach themselves from one another, and, by 

 separating, form distinct white spots on the dull 

 green base of the rock. The uncertainty of the 



* Dolomieu by no means excels in literary composition, his sen- 

 tences being very tedious and complex. His long notes, which only 

 distract the attention, are here thrown into the text. 



