336 THE ROMAN CAMPAGNA 



ance of the western portion of its rim, the great size 

 of its crater compared with the total height of the 

 mountain, and the existence of a later cone and crater 

 inside, together with a number of craters outside, 

 suggest that the energy of the volcano culminated in a 

 gigantic explosion, whereby the upper half of the cone, 

 perhaps twice as high then as it is now, was blown 

 away, leaving inside a yawning chasm or caldera that 

 opened towards the west, where the wall was broken 

 down. Such a paroxysm is known to have occurred 

 in the history of other volanoes. In the case of 

 Vesuvius, for example, Monte Somma remains as a 

 fragment of the earlier and ampler condition of the 

 mountain, before the catastrophe in which the upper 

 part and the southern half of the cone were blown 

 away. Since that event a new and smaller cone, 

 forming the present Vesuvius, has been piled up on 

 the southern segment of the old crater-rim. 



The explosion that eviscerated the Alban volcano 

 must have caused widespread desolation over the sur- 

 rounding country. It was not improbably followed 

 by a long interval of repose. But the subterranean 

 energy was not exhausted, though it never again 

 showed itself on so vigorous a scale. We can trace, 

 indeed, the signs of its gradual enfeeblement. When 

 it recommenced its activity the vent, which served as 

 the channel by which its eruptions took place, still 

 retained its central position. Round this vent a new 

 but much smaller cone, bearing witness to less vigour 

 of eruption, was built up in the middle of the crater. 

 This younger mass rises in Monte Cavo to a height 

 of 3150 feet, the highest elevation on the whole 



