DOMAIN X. TRANSILIENT. 



cannot have on the surface of mountains, where 

 the weather, and a thousand other causes of de- 

 gradation, alter the hardest rocks. If I have 

 acquired some knowledge of the nature of rocks, 

 I owe it in a great measure to the comparisons 

 that I have heen able to make from the observa- 

 tions furnished by the monuments of Rome, 

 with those which I collected in the mountains : 

 and I cannot too much advise all naturalists, 

 who travel in Italy, to pursue a regular course 

 of lithology on those large masses, whose ex- 

 traction is a proof of the industry and power of 

 that ancient people who used them, and of which 

 the beauty seems to assure a sort of pre-eminence 

 to the eastern regions which furnished them : 

 and this advantage which they possess over ours, 

 is doubtless owing only to the scantiness of 

 means that we have employed to find similar 

 substances in our own mountains; thus how 

 ridiculous our magnificence appears, when we 

 compare it with that of the ancients ! I have 

 made a descriptive catalogue of all the monu- 

 mental rocks of ancient Rome, which perhaps 

 may not be uninteresting. 



" It is besides easy to show that the bases of 

 many porphyries are only disguised granites; 

 and it is sufficient to take off the kind of mask 

 which covers them, and which depends on the 



