THE PHLEGILEAN FIELDS 329 



Bracciano volcanoes, even when these were at the 

 height of their vigour. It can be followed in numerous 

 detached tracts of valley-floor through the hills east- 

 wards to Sora, and southwards to near Gaeta. There 

 is reason to believe, indeed, that the type of small 

 submarine vents extended all through the volcanic 

 tract from its northern to its southern limit. 



A little reflection will show that the sites of these 

 vents may be expected to be difficult of detection. 

 In the first place, though numerous, their small size 

 may easily make them escape notice, even where they 

 may have been wholly or partially laid bare by de- 

 nudation. Probably a close parallel to their original 

 forms and to the way in which they were in some 

 places crowded together is to be found in the Phle- 

 graean Fields near Naples a district which well 

 deserves the careful scrutiny of any one who desires 

 to follow the volcanic history of the Roman Campagna. 

 Its cones are terrestrial, indeed, not submarine. Being 

 much younger, they have been far better preserved 

 than those of the submarine stage of the period. 

 One of them, Monte Nuovo, though now as cold 

 and silent as the oldest of them, was thrown up so 

 recently as A.D. 1538. Another, that of the Solfatara, is 

 still a steaming vent, while Vesuvius from time to 

 time vigorously asserts its claim to rank in the list of 

 active volcanoes. These Neapolitan cones probably 

 convey a fair idea of the general distribution and 

 aspect of those of the Campagna, especially in the 

 later time when the volcanic platform had eventually 

 been raised above the level of the Mediterranean. We 

 see, as in the case of the youngest and smallest of the 



