In all these districts, Professor Mercalli distinguishes several well-marked seismic centres, to each of which he traces the origin of two or more earthquakes. In the districts with which we are at present concerned, those of the Alpes Maritimes and the western Riviera, the most important centres are situated near Oneglia (in the sea), near Taggia, in the valleys of the Vesubia and Tinea (near Nice), and in the sea to the south of Nice. To the first of these centres belongs the disastrous earthquake of February 23rd, 1887, as well as its after-shocks on February 24th, May 20th, July 17th, and September 30th of the same year, also the ruinous earthquakes of 1612 and 1854, and several others of a lesser degree of intensity. All of these were longitudinal earthquakes, the axes of their meizoseismal areas being parallel to the neighbouring mountain-ranges. A few miles to the west of Oneglia lies the Taggia centre, with which were connected the disastrous earthquake of 1831, the violent earthquake of 1874, and other strong or very strong shocks. These were for the most part transversal earthquakes, their axes being perpendicular to those of the Oneglia centre. Some of the strongest earthquakes in this region originated in a centre lying to the north of Nice in the valleys of the Vesubia and Tinea. Among them may be mentioned the ruinous earthquakes of 1494, 1556, 1564, and 1644, and probably also the disastrous earthquake of 1227. A fourth centre, and one of considerable interest, is that which lies at sea, a short distance to the south of Nice, and nearly along the continuation of the valleys above-mentioned. This is the secondary centre of the earthquake of 1887, and probably also of that of December 29th, 1554. It is occasionally in action apart from the Oneglia centre, as on November 27th, 1771, June 19th, 1806, and December 21st, 1861; but such shocks, though rather strong, never reach a high degree of intensity. _Origin of the Earthquakes of 1887._--The most important feature in the principal earthquake of 1887 is its origination in two distinct foci, which are sometimes in action almost simultaneously, but more often separately. The earthquakes belonging to the two foci differ greatly in intensity and number, and the stronger part of the shock in 1887 originated in the focus associated with the more disastrous and more frequent earthquakes.