THE ALBAN HILLS 335 



animals, that the manifestations of volcanic energy 

 reached their climax. Instead of finding outlets in 

 many minor vents that discharged showers of ashes 

 and stones, it now broke out in a few large orifices 

 from which not only copious discharges of frag- 

 mentary materials, but also streams of lava were 

 emitted. In the district around Rome this greater 

 localisation and more violent activity were specially 

 concentrated in two areas separated from each other 

 by an intervening plain about thirty-five miles broad. 

 On the south side of this plain, the group of the 

 Alban Hills was built up by many successive erup- 

 tions ; on the north side, a chain of important vents 

 stretched from Bracciano northwards to the great 

 crater of Bolsena. Of these two areas, the southern 

 comes more closely into connection with Rome and 

 the Campagna, and as it tells its story vividly and 

 fully, it claims our more special attention. 



The Alban Hills, so striking a feature in the scenery 

 of the region and so indissolubly associated with the 

 early chronicles of the Eternal City, consist essentially 

 of one great volcanic cone of the type of Vesuvius, with 

 a base about twelve miles in diameter. This cone has 

 been so greatly truncated that its summit, from one 

 side of the rim to the other, measures about six miles. 

 The highest point of the rim is 3,071 feet above sea- 

 level. Inside lies the huge cauldron-like depression 

 that formed the original crater of the volcano, encircled 

 with steep slopes and rocky walls save on the north- 

 west side towards Rome, where the continuity of the 

 crater-ring has been destroyed. 



The abrupt truncation of this cone, the disappear- 



