rr.lLIAiV PETROLOGICAL SKETCHES 545 



character of both the exterior Latera and interior Mczzano 

 craters are better preserved than in the case of Bolscna ; and 

 also because it is, according to Stoppani, at present in a solfataric 

 state.' The lavas of Latera are entirely leucitic, so far as is 

 known, no trachytes having yet been found at this center. 



To the north of the Bolsena Region lie a number of small 

 isolated volcano vents, such as the "trachytic" Monte Amiata 

 and the basaltic hill of Radicofani. To the east are the Tertiary 

 deposits flanking the main line of the Apennines, and to the 

 south lies the closely similar volcanic Viterbo Region, which will 

 form the subject of the next paper. 



As to the character of the eruptions little need be said here, 

 though I may insert de Stefani's summing up of the subject. He 

 savs :" "In conclusion we can hold that the volcano, submarine 

 in the beginning, became later subaerial and erupted in the 

 midst of a low and swampy region like the Maremme (marshes) 

 of the present day in the same country." He thinks that the 

 latest eruptions of tuff were dry and probably fell on dry land. 



Discussion of the origin of the lake must be deferred to 

 another place, since the existence of such crater-lakes is a feature 

 common to several of the regions to be described. We may 

 note, however, that there are two prominent theories. One is 

 that of vom Rath and Verri, who regard the lake as a sunken 

 tract, the sinking being due to the ejection of material from 

 various points which forms the hills surrounding it. The other 

 is that held by Stoppani and de Stefani, who consider the lake 

 as the volcanic center, the remains of a large crater which has 

 been enlarged by explosions and the falling in of its walls ; and 

 from which was ejected the greater part of the volcanic material, 

 small flank eruptions also adding to the mass of the volcano. I 

 may remark, in anticipation, that the weight of evidence and 

 analogy is in favor of the latter theory. 



' As I did not visit this western part of the region I cannot say whether one 

 crater circle cuts the other or not, and I can find no mention of this point in the 

 literature. 



^Dk Stefani, op. cit., 526. He notes that von Buch expressed the same view 

 about 1810. 



