Physical Structure of the Site of Rome. 28 



Lacus Nemorensis, now filling the craters from which these lava 

 currents flowed*. 



A line of connexion may be traced between the volcanic 

 mountains of Teanum and Ilocca Morfina, in the Campi Phle- 

 grsei, and those of Latium, streams of compact lava having burst 

 forth in many places in the Campagna, as at the modern town ot 

 Pofi, near the junction of the Tolero with the Garigliano, where 

 it Hes upon the Subapennine clay of marine origin, — in the midst 

 of the apennine limestone, in the country of the Hernici, near 

 Veroli, between Frusino'and Ferentinum ; at the modern Ti- 

 chiena, where there is an ancient crater, — and close by the La- 

 cus Regillus. A current of lava has been traced by the side of 

 the Appian Way, from the volcano of the Alban Mount to 

 within two miles of the gates of Rome, about three quarters of 

 a mile from the spot where the tomb of Caecilia Metella stands, 

 a distance of six miles. It is of different dimensions in different 

 places, but in the quarries nearest Rome, it has been found above 

 60 feet in thickness. It has long supplied, in ancient as well as 

 in modern times, the paving-stones of Rome; and there are 

 numerous quarries in it, along the whole of its course. It is 

 important, also, to remark, that this stream of lava lies upon a 

 mass of volcanic lapilli f. Basaltic lava has also been met 

 with about seven miles from Rome, on the Via Ardeatina. 



Passing over the country north of the Tiber, we find other 

 sites of extinct volcanoes. The Lacus Sabatinus was once the 

 crater of a volcano, and is now surrounded by hills of soHd 

 lava, sending forth numerous currents into the surrounding 

 country. Between this lake and Centum Cellae, the modern Ci- 

 vita Vecchia, there is a chain of hills, at the eastern end of which, 

 at Tolfa, there is a lava current, in great vertical masses, break- 

 ing through limestone. The main part of the ridge is a transi- 



• The mysterious rising of the waters in the Alban Lake, may be very ra- 

 tionally accounted for, by some partial volcanic action in this region. 



•f- " There are some passages in ancient writers, which might lead us to 

 suppose a volcano to have existed among these mountains, even at a period 

 within the limits of authentic history; for Livy notices a shower of stones, 

 which continued for two entire days, from Mons Albanus, during the second 

 Punic war, * Albano Monte biduum continenter lapidibtis pluit.' Julius Obse- 

 qucns, in his work de ProdigiiSy remarks, that in the year 640 ab U. C. the 

 hill appeared to be on fire during the night."— Z)aw*e;*y on Volcanoes, p. 1 30.J 



