4 THE ROMAN COMAGMATIC REGION. 
towns of San Lorenzo and Acquapendente. On the east the hills are of a fairly 
uniform height of 600 to 650 meters, the town of Bolsena lying on the northeastern 
shore, and the city of Orvieto some 14 kilometers northeast of the lake, on the edge 
of the igneous area. The town of Montefiascone is situated on a hill (633 meters) 
near the southeastern corner of the lake. On the south the hills are low, uniformly 
less than 100 meters above the lake-level. On this shore are the villages of Marta 
(at the lake emissary) and Capodimonte, while 15 kilometers to the south is the 
town of Toscanella. The western hills are also low, though somewhat higher than 
on the south, with the town of Valentano near the southwestern corner. 
From this encircling crest of hills the land surface slopes down to the north, 
east, and west, the fall being quite regular, but somewhat diversified by the remains 
of cones and craters. As the rocks are to a large extent somewhat incoherent tuffs, 
the general topography is characterized by erosion ravines, radiating from the lake, 
and often leaving isolated buttes here and there. 
To the west of Lake Bolsena is another, though much smaller, depression, or 
rather plain, surrounded by a girdle of hills, whose circle impinges on that of 
Lake Bolsena. In this is the small Lake Mezzano, and the whole, undoubtedly a 
distinct crater, is known as the Latera Volcano, from a small town on its rim. A 
prominent feature of this is an extensive and very rough-surfaced lava flow, now 
covered with forest, and known as the Selva del Lamone. Owing to bad weather 
I was unfortunately unable to visit the Latera Volcano, though my examination of 
the rest of the district was fairly complete. 
The general structure of the complex (and especially the origin of Lake 
Bolsena) has long been the subject of dispute, and unfortunately the two geologists 
who have studied the district most completely (Moderni and Sabatini) do not 
hold the same views. According to Moderni, the Vulsinian complex has been 
formed by the eruptions from four principal vents the volcanoes of Latera, Bolsena, 
Montefiascone, and Capodimonte the first three being situated, respectively, on the 
west, northeast, and southeast, and the last being to a large extent now covered by 
the waters of the lake in its southern part. Each of these volcanoes had its own 
smaller flanking and parasitic cones. Lake Bolsena, according to his view, is not 
a true crater lake, due to either the explosion or the falling in of a single large vol- 
canic cone, but rather a lake basin formed by the accumulation of the materials 
ejected from the four surrounding volcanoes. 
On the other hand, Sabatini regards the complex as essentially a system of 
concentric crater ridges and atrios, due to the gradually decreasing vulcanicity 
about one main central vent, of which Lake Bolsena is the crater. Superposed on 
the flanks of, and later than, this main volcano are the smaller ones of Latera, Bol- 
sena, and Montefiascone, with their parasitic cones. 
It is unnecessary here to weigh these two opinions, so diametrically opposed in 
some respects. Each represents the conclusions of an able geologist who has made 
a careful and profound study of the district, Moderni more especially of the western 
