We shall next present the reader with a sketch of the history of some of the volcanic vents dispersed throughout the great regions before described, and consider attentively the composition and arrangement of their lavas and ejected matter. The only volcanic region known to the ancients, was that of which the Mediterranean forms a part; arid they have transmitted to us very imperfect records of the eruptions in three principal provinces of that region, namely, the district round Naples; that of Sicily and its isles; arid that of the Grecian Archipelago. By far the most connected series of records throughout a long period relates to the first of these districts; and these cannot be too attentively considered, as much historical information is indispensable in order to enable us to obtain a clear view of the connexion and alternate mode of action of the different vents in a single volcanic group. The Neapolitan volcanos extend from Vesuvius, through the Phlegr æ an Fields, to Procida and Ischia, in a somewhat linear arrangement, ranging from the north-east to the south-west; as will be seen in the annexed map. (PI. 3.) Within the space above limited, the volcanic force is sometimes developed in single eruptions from a considerable number- of irregularly scattered points; but a great part of its action has been confined to one principal and habitual vent, Vesuvius or Somma. Before the Christian era, from the remotest periods of which we have any tradition, this principal vent was in a state of inactivity.