338 THE ROMAN CAMPAGNA 



flank. A few minor craters have been opened on its 

 east side, and all round there still rise warm springs 

 and emanations of sulphuretted hydrogen. To the 

 north of this great vent lies another of similar charac- 

 ter and origin but of smaller size, which now con- 

 tains the Lago di Vico. The surface of this lake, 

 which stands at a height of 1,663 ^ eet above sea-level, 

 is encircled by a crater-wall which on the west side 

 mounts to nearly 1,600 feet above the sheet of water 

 which it encircles. To the northeast rises the volcanic 

 mass of Monte Cimino, 3,464 feet high. Still farther 

 north is the largest of all the Italian crater-lakes, the 

 Lago di Bolsena, which is no less than twenty-eight 

 miles in circumference. 



Having regard to the great variety of material in 

 these different volcanic piles and to the evidence fur- 

 nished by them that they were formed by many 

 successive eruptions, perhaps separated from each 

 other by long intervals of time, we cannot but be 

 impressed with the antiquity of the great subaerial 

 cones and the protracted period required by each of 

 them for its formation. We must remember, too, 

 that from the very beginning of their history they were 

 ceaselessly attacked by the various agents of subaerial 

 erosion. The first showers of rain that fell on their 

 young slopes of incoherent ashes gathered into runnels 

 which would plough furrows in their descent to the 

 plain. Century after century these watercourses were 

 cut deeper and wider until they have attained the 

 dimensions of the numerous fossi that now radiate from 

 each crater-rim. In some cases these lines of erosion 

 served as channels for the streams of lava that were 



