544 HENRY S. WASHINGTON 



Surrounding the lake and sloping steeply down to its waters 

 (leaving only a narrow shore margin), is a girdle of hills whose 

 most elevated points on the north are 600 to 680 meters above 

 sea level, and hence 300 to 375 above the surface of the lake. 

 Towards the south they diminish in height, a feature which 

 this crater possesses in common with others of Italy. 



These hills are made up of volcanic material, chiefly leucitic 

 lavas and tuffs, though to the north of the lake considerable 

 " trachyte" is found. In places fine sections of superposed tuffs 

 and lava streams are exposed, and in the latter a columnar struc- 

 ture is sometimes very well developed. From the crest encirc- 

 ling the lake the surface slopes gradually down on all sides, till 

 the volcanic ejectamenta thin out in tuffs resting on the Sub- 

 Apennine pliocene marine marls. 



The whole district occupied by volcanic material thus forms 

 a low lenticular mass (with the lake in a hollow at the center) , 

 whose outer sides slope at angles of 12° to 15°. Its diameter is 

 about 40*"" and its total area some 1300 square kilometers, as 

 has been estimated by Stoppani and Verri. Erosion of the 

 soft tuffs has cut up the surface to a great extent, producing 

 characteristic radiating ravines, which de Stefani compares with 

 our western canyons in miniature, and forming isolated buttes 

 such as those on which the towns of Orvieto and Civita di Bag- 

 norea are so picturesquely situated. 



Lying immediately to the west of Lake Bolsena is another 

 depression, or rather plain surrounded by a girdle of hills, also 

 of least height to the south, its circle impinging on that of the 

 Bolsena Crater. This crater, which is known as the Latera 

 Crater, is smaller than that of Lake Bolsena, having a diameter 

 of about 7^°". The small Lake Mezzano, which occupies part of 

 the area, preserves well the form of a crater, and may be looked 

 upon as the site of the last eruption of the Latera volcano. This 

 seems, from the descriptions, to be a distinct eruptive center, 

 though nothing is said by any of the writers mentioning it as to 

 its age relative to that of the Bolsena volcano. It would seem, 

 however, to be the more recent, since the original crateriform 



