38 On the Styles of Building in ancient Italy ^ and 



comment on its durability. The reddish colour which it as- 

 sumes at Rome is undoubtedly owing to the presence of iron 

 in the sulphureous springs, which is decomposed, as pyrites al- 

 ways are, by exposure to the weather. 



V. Silice, or selce, as it is known to the Italians, is not the 

 true silex ; but ancient lavas and basalts. It was known by 

 the same name to the Romans, as is universally admitted ; 

 but will be illustrated by the accompanying interesting in- 

 scription of Trajan, on a milestone of the via Appia, which 

 every one knows was paved with basalt : — 



VI 



IMP CAESAR 



DIVI NERVAE 



FILIVS NERVA 



TRAIANVS AVG 



GERMANICVS 



DACICVS 



PONTIF. MAX. 



TRIR. POT. XIII 



IMP. VI. COS. V. P. P 



XVIII. SILICE SVA PECVNIA 



STRAVIT 



This inscription I copied at Mesa in the Pontine Marshes. 

 The streets of Rome and all the vice in the neighbourhood were 

 paved with this lava, from the famous Coulee of the Capo di 

 Bove, where immense quarries anciently dug may still be seen. 

 The Via Ostensis may still be seen near Ostia, paved with this 

 same lava, which comes from the Capo di Bove, two miles 

 from Rome, and therefore carried sixteen or seventeen miles, 

 and certainly not from the Alban Mount, as Ferber imagines, 

 which is greatly farther distant. According to Daubeny, in 

 his excellent work on volcanos, this coulee " appears to consist 

 of an intimate mixture of augite and leucite, either in crys- 

 tals or granular masses, the former of a bottle green colour, 

 passing into brown, the latter white or azure." I must 

 refer to the work itself for the mineralogical and geological 

 peculiarites of this remarkable formation, taking leave at the 

 same time strongly to dissent from the author, as to the source 

 from whence he takes its origin. A treatise has been published 

 expressly on this kind of stone, " Lupi, del selce Romano.'' 9 



VI. Pomice, Pumex, Pumice. This stone, which Nibby 



