426 PHYSICAL GEOGRAPHY. 



also be added the pumice, sand, and ashes, scattered not only over the whole island, but 

 to a distance of 300 miles round, in such abundance as to destroy the fisheries in the 

 neighbouring sea. With these additions it would amount, we may believe, to fifty or sixty 

 thousand millions of cubic yards, exceeding the solid contents of Hecla, which, if six miles 

 in diameter at the base, and 1 700 yards high, would contain nearly fifty thousand millions 

 (49,537,270,000) of cubic yards. This is probably larger than any individual mass of the 

 older igneous rocks known to exist." This one discharge of this volcano, if spread over 

 the coal fields of Great Britain, would cover them with a coating of basaltic rock twenty 

 feet thick, or accumulated together upon the site of London, the product would be a 

 mountain rivalling the Peak of Teneriffe. 



Besides the deposition of horizontal beds of ejected matter, the bulging up of the 

 surface in the form of cones and hills of considerable elevation and diameter, on the flanks 

 of volcanic mountains, or on plains subject to volcanic action, is a common instance of 

 change wrought by the mighty disturbing force exerted. . Thus the entire volcano of 

 Jorullo arose out of a plain to the west of Mexico, to the height of 1680 feet, the sur- 

 rounding district, through an area of three or four miles, being swelled up like a bladder, 

 studded with cones of inferior size. The formation of Monte Nuovo in the neighbour- 

 hood of Naples, and of Monte Rossi upon the side of Etna, are instances of similar pheno- 

 mena. Extensive subsidences also frequently attend volcanic eruptions. The greater 

 part of the Papandayang, on the western extremity of Java one of the largest volcanic 

 mountains of the island was swallowed up in the year 1772. On the night of this 

 event, the inhabitants on the declivities and at the foot of the mountain were alarmed by 

 the appearance of a luminous cloud, which seemed to envelop the higher regions ; but 

 before they could retire from the vicinity, the mass began to give way, and disappeared 

 with a tremendous noise in the earth. An extent of ground belonging to the mountain 

 itself and the environs, fifteen miles long and six broad, subsided by this convulsion. 

 The formation of cracks and fissures is another feature of change effected by volcanic 

 agency. In 1669, in the plain of St. Lio, upon the side of Etna, a fissure six feet broad 

 and of unknown depth opened with a loud crash* traversing a length of twelve miles, and 

 emitting a vivid light, indicating the presence of incandescent lava. Five other parallel 

 fissures also opened, extending a considerable way ; and the same effect has been often 

 produced by the paroxysmal excitement of Vesuvius. The external appearance of active 

 volcanic mountains is thus in a state of striking instability ; and in not a few instances 

 great changes may be traced, both of form, elevation, and magnitude. Though the alti- 

 tude of Etna may not have materially varied during the last 2000 years, yet the cone has 

 repeatedly fallen in, and been reproduced. It was 320 feet high in the year 1444, but 

 fell in during the earthquake of 1537; and, after reproduction, the cone lost so much of 

 its height in 1693, that, from several places in Val Demone, it ceased to be visible where 

 it had been seen. The summit of Vesuvius, about a quarter of a century ago, was a 

 rough and rocky plain, covered with blocks of lava and scoriae, and cut by numerous 

 fissures, from which clouds of vapour were evolved. These were all removed by the 

 violent eruptions of October 1822; and a vast elliptical chasm was formed, three miles 

 in circumference, three quarters of a mile in the longest diameter, and about two thou- 

 sand feet deep. Upwards of eight hundred feet of the ancient cone were carried away, 

 which reduced the height of the mountain from 4000 to 3200 feet. But whatever changes 

 may have transpired within the period embraced by the records of history, they are 

 utterly insignificant to those anterior to that date, of which the geological appearance of 

 Etna exhibits indisputable evidence. All the most conspicuous of its eighty lateral cones 

 are older than the era at which authentic history commences, and bear witness to violent 

 catastrophes in the hoar antiquity of time ; and as one in three eruptions is supposed to 



