Page:Popular Science Monthly Volume 69.djvu/568

564 Bishop of Ostia, as Leo Ostiensis, one of the most sober and important of Italian historians; the 'Annales Cavenses' (569-1318), produced by another famous monastery near Salerno; and finally the 'Chronicon' (1102-1140) of Falco of Benevento, notary, judge and papal chancellor, to whom posterity is indebted for precious information. These contemporary sources contain all that is known of the ninth and tenth Vesuvian eruptions. Details are wanting, but it is said of the former that it happened in January, 1037, and lava flows reached the sea; the duration of the latter (1139) is stated in one account to have been eight, in another, forty days. Critical estimates of the documents above referred to will be found in various works dealing with the sources of medieval history, amongst which it will be sufficient to mention an article by Hirsch on 'Desiderius of Monte Cassino.' Our review of the chronology of eruptions in the early middle ages is now completed.

There remains to be considered a question that has often been asked, and variously answered: was the form of Somma-Vesuvius essentially the same in antiquity as we know it to-day, or were the ancients acquainted with only a single crateriform summit whose broken wall now partially encircles the newer cone? The only reason for raising the inquiry at all is that neither by direct statement nor by implication do any of the ancient authors allude to Vesuvius as a double-peaked mountain, and the older topographic descriptions can with difficulty be reconciled with the present form of the volcano. It appears indeed passing strange that Strabo, Pliny, Cassius Dio and Procopius should all have remained silent respecting the most salient feature of Vesuvius as viewed from the west, in case its twin peaks presented to their eyes, as they do to ours, almost identical outlines. Yet, accepting their accounts at face value, the only conclusion possible is that the younger cone has been entirely built up during the middle ages, a far shorter interval than is demanded by geologic evidence. A time allowance of barely a thousand years (or at the most fifteen hundred, if we leave Procopius out of the reckoning and admit the correctness of Leone di Ambrogio's figure of a double summit in 1514) for the formation of the central cone is absurdly inadequate, the number of eruptions contributing towards it too few, and their intensity too slight, to have performed the work. This we know from the present slow rate of accumulation, and from the relatively unimportant changes wrought by even paroxysmal eruptions. And it may well be doubted whether the convulsion of 79 A. D. was of more violent character than those of 1631 and 1906, these three exceeding all others in intensity.