NOME XI. GRANITE AND GRANITIC PORPHYRY. 185 



of the base, in which there is some appearance, 

 of a solution of continuity. 



" There are porphyries in which these spots, 

 which differ by their colour and texture from 

 the base of the rock, are so multiplied that they 

 resemble bricias, and receive from them the epi- 

 thet of Porfidi briciati. They appear formed of 

 an infinity of similar pieces, which become 

 united by a common cement. This kind of por- 

 phyry seems to me to depend on some accidents, 

 which have disturbed the coagulation ; which 

 has been suspended and resumed at several 

 times. 



" I mention, with equal confidence, the im- Monuments of 



Rome. 



mense blocks of rocks of different natures, which 

 decorate the city of Rome, or are found in its 

 ruins, as I would mention the mountains them- 

 selves from which these rocks have been extract- 

 ed ; because it is seldom that nature herself ex- 

 poses masses so large, and in such perfect pre- 

 servation ' y and to obtain them thus, it has been 

 necessary to attack the heart itself of the moun- 

 tains. Columns of granite from 40 to 50 feet in 

 elevation, sarcophages hollowed in masses of 

 porphyry to the extent of even 1000 cubic feet, 

 present as much matter for observation as the face 

 of a rock naturally exposed ; and they show the 

 substances in a state of preservation which they 



