1814.] Account of the Mountains of ancient Lallnm. n'J 



olivine, as far as I myself have observed. It is split into irregular 

 masses, and occurs in many places, though it never constitutes 

 entire hills. & ma ll rivulets of it are seen near Kocca di Papa 

 towards the chapel, called Madonna del Tufa. It occurs also 

 scattered over the whole summit of the Tusculan mountains, par- 

 ticularly on the rock on which Rocca Priora is built : but the 

 greatest masses of it occur at the bottom of the Tusculan moun- 

 tains, constituting oblong hills, which run out into the Roman 



plti) 11 . 



Nor is the region in which the peperino prevails without a por- 

 tion of compact lava. For it is not only found at the foot of the 

 lull winch ooks towards the Roman plain, as at the Gro'ta Ferrata 

 and the place called Alle Fratocchie, below the city of Albano- 

 hut what is surprising, it covers in several places cliffs composed of 

 peperino, which surround the lakes Albanus and Neraorensis con- 

 stituting rocks which rise perpendicularly from the shore of the 

 akes to the margin of the crater, so that one would be tempted to 

 believe that the whole crater is formed of lava, over which the 

 peperino has been deposited. The lake Neraorensis is not only 

 almost surrounded by compact lava, but at the part lying below 

 Nemi, and mount Albanus, it is decorated by rocks" composed of 

 sperone, through which the fountain of the nymph EgemTuns 



ine peperino and compact lava are seldom immediately under 

 the surface of the ground. They are commonly covered With 

 other volcanic products The lava sperone, the nearer the surface 

 W f, becomes not only more porous and soft, but composed of 

 d.s. net fragments about the size of a nutmeg or walnut, confu- 

 ted together, and forming beds generally parallel to the decli- 

 p"L »'e mountain, as maybe very well seen at the Rocca di 

 1 ..pa. At length ,t acquires the aspect of pumice ; but differs from 

 it n having nothing fibrous in its structure. These scoriaceous 

 beds may be observed at the chapel oi Madonna del Tufa, near 

 the lake Nemi, and in the Tusculan mountains. They are fre- 

 quently covered with a fat reddish earth. 



The compact lava is also frequently mixed with a reddish earth 

 not^ofat in its feel as the preceding/ It is employed in the maling 



WoW von Buch has, in an excellent book,* given the name 



/, , M. .?u tbe M ° ntl Venli ' and of th « dentine and 



Capit ohM hilb, winch must certainly be considered as a volcanic 



<> and« very nuhr to the volcanic tuff of Naples, only a 



lutlc harder Yet the earthy texture, and the mixture of reddish 



pumice, sufhcau.ly distinguish it from that mineral. Under the 



;■»'■ voh-a....- tuff, he designates very different substaaces found in 



; '""' ol Rome j namely, fragments of pumice, puzzuolana" 



•""' *« owunon volcanic earth, ashes, and wbbi All these 



/.;.,' :.;'.T::;; '"• »**^- ■* ■*■** i^u^ „*, „„„,,,. 



