The seismic vertical, Mr. Mallet determined from the independent and concurrent evidence of above seventy separate wave-paths, was close to the village of Cag,giano, near the eastern extremity of the valley of the Safaris. The depth of the focal point below the sea-level, that is, the mean focal depth was found to be about 5! geographical miles. From all the information, observed and calculated, it was deduced that the focal-cavity, within which the seismic energy originated, was a curved lamellar cavity, or fissure, of about three geographical miles in depth by nine in length, with an inclined vertical section, and a mean focal depth (or depth of its central point of surface) of 5i miles below the level of the sea, as just stated. The probable horizontal form of the cavity; when laid down upon a map, co-ordinates with the existing lines of dislocation of the country in a remarkable manner. Mr. Mallet, it may here be remarked, assumes the force that acted within this cavity to have been due to steam of high tension, either euddeuly developed or suddenly admitted into a fissure rapidly enlarged by rending.
The most trustworthy of the observations of time correspond with considerable exactness, and give a velocity of transit of the wave of shock upon the surface, of between 700 and 800 feet per second. Strictly speaking this is the velocity at which the ware form was propagated from point to point. The velocity of the wave itself, or of the wave particle was in round numbers between 13 and 14 feet per second in the direction of the wave-path. Mr. Mallet points out a remarkable relation between this velocity and that recorded for the earthquake of Riobamba, as the greatest whose effects have been ob served. The height due to the velocity of this wave is to the altitude of Vesuvius as that due to the velocity recorded of the Riobamba wave is to the mean height of the volcanic shafts of the Andes, and more especially to the height of the volcanic vents nearest to Riobamba.
[Votcallos.] The wave of shock, of course, decays in relation to superficial distance from the seismic vertical. The amplitude of the wave slowly and slightly increases, and its velocity decreases. In the case of the Italian earthquake under investigation, the lowest velocity at nearly 30 miles from the seismic vertical was still about 11,1 feet per second. The total modifying effects of this earthquake on the earth's surface were Insignificant. No great sea-wave accompanied it ; nor was such possible, the focal point being inland. Mr. Mallet examined with care more than 150 miles of sea-coast, as well as river-courses, for evidence of any permanent elevation of land having taken place con currently with the earthquake, but found none. This is an important point, because geologists and travellers have often ascribed elevations of the land to earthquakes, or to a succession of earthquake-shocks directed upon the mine spot ; but " earthquakes," Mr. M. observes, " cannot produce elevations, although the latter have been known to have taken place about the same time as earthquakes, and in the same region." . . . . " The functions of elevation and depression," of an earthquake, "are limited solely to the sudden rise and as immediate fall, of that limited portion of the surface through which the great wave is actually passing momentarily." The works and memoirs cited in this and in the article EARTH QUAKE, will make the student acquainted with the entire available literature Em the subject of earthquakes.