llti Account of the Mountains of ancient Lai htm. [Arc. 



origin of peperino is, that it often contains pieces of charcoal,* 

 which cannot he distinguised hy the vulgar. It contains likewise 

 wood not charred, hut rendered pale and similar in appearance to 

 amianthus. 



From what I have said, it is obvious that peperino is composed 

 of fragments of very different minerals, agglutinated at a time- 

 when this part of the earth was covered with trees. Whence 

 these fragments and the cement came will appear as we proceed. 



Peperino, along with a peculiar spongy lava, which the Romans 

 call sperone, and with a little compact basaltic lava, which they 

 denominate selce, forms the congeries of mountains that constitute 

 Old Latium, and which, almost touching the Appenines at Prte- 

 neste, separate the plain of Rome from the Pontine marshes. 



This porous lava, the mass of which contains a prodigious num- 

 ber of small opaque leucites, many augites, and some mica, is 

 perforated by a great number of long irregular pores, the surface 

 of which is unequal and dull. This lava sperone constitutes the 

 greatest part of these mountains, and particularly all the Tusculan 

 mountaius, from Tusculum (called at present Frascati), as far as 

 Corbium (at present denominated Rocca Priora), mount Albanum, 

 the highest of all (tnonte Lazio or Cavo), and the rock in which 

 the village called Rocca di Papa is situated. If any inference can 

 be drawn from external form, and from their connection with the 

 others, mount Algidus, likewise parallel to the Tusculan moun- 

 tains ; mount Artcmisius, lying towards Velitrae ; the mountains 

 Ariani ; and the mountain called La Fajola, are composed of the 

 same lava. 



The peperino, beginning at the bottom of mount Alhanus arid 

 Artemisius, between south and west, surrqunding the lakes Alha- 

 nus (la«o d'Albuno), and Nemorensis {lago di Nemi), with a high 

 and steep border, gradually sinks into the plain of Rome towards 

 the sea snd Velitras. But besides these lakes, there is a valley 

 particularly worthy of attention, called Valle Riccia, situated 

 below the village Aricia. This valley has an oblong bason form 

 shape, and is surrounded with steep rocks, except towards the sea. 

 It is said to have formerly constituted a lake. 



The mountains composed of sperone differ from those consisting 

 of peperino, chiefly in forming high and long ridges, very steep, 

 and without any traces of a crater. The peperino hills are not so 

 high, broader; slope gently, and in the centre exhihit a lake or 

 concavity, which may be conceived as the remains of a former 

 crater. 



The compact lava, which is seldom entirely free from pores, 

 when it contains them in abundance becomes exactly similar to the 

 sperone. Its colour is usually grey. It contains always augites, 

 almost always leucites, often mica, seldom felspar, and never 



» Riccioli, a dealer in minerals in Rome, lias a specimen of charcoal in pepe- 

 rino an inch thick, and nearly five inches long. 



2 



