The existence of two foci would of course give rise to a meizoseismal area elongated in the direction of the line joining them. It is clear, however, that the Oneglia focus was also extended in the same direction; for, in the after-shock of February 24th, the isoseismals drawn by Professor Mercalli are parallel to this line; and this was also the case in the shock of March 11th. As both foci were under the sea, it is difficult to locate them with precision; but it seems very probable that they occupy portions of a submarine fault that runs parallel or nearly so to the Apennine axis between the meridians of Oneglia and Nice. A brief period of preparation is a characteristic of the Riviera earthquakes. In 1887, two at least of the preliminary shocks on February 23rd (those of about 2 and 5 A.M.) originated in the Oneglia focus. At 6.20 A.M. the first and weaker movement took place in the western focus; and, a few seconds after the resulting vibrations reached the eastern focus, the second and greater slip took place there. The occurrence of seismic sea-waves is probably evidence of the formation of a small, though sensible, fault-scarp in the same region. To relieve the additional stresses thus brought into action along the fault-surface, numerous small slips took place in different parts, some as far to the west as the Nice focus, but the greater number probably within or close to the focus in the neighbourhood of Oneglia. REFERENCES. 1. BERTELLI, T.--"Osservazioni fatte in occasione di una escursione sulle Riviera Ligure di ponente dopo i terremoti ivi seguiti nell' anno 1887." _Boll. Mens. dell' Oss. di Moncalieri_, vol. viii., 1888, Nos. 6, 7, 8. 2. CHARLON, E.--"Note sur le tremblement de terre du 23 février 1887." _Bull. del Vulc. Ital._, anno xiv., 1887, pp. 18-23. 3. DENZA, F.--_Alcune notizie sul terremoto del 23 febbraio 1887_ (Turin). 4. ISSEL, A.--"Il terremoto del 1887 in Liguria." _Boll. del R. Com. Geol. d'Italia_, anno 1887, supplemento, pp. 1-207. 5. MERCALLI, G.--_I terremoti della Liguria e del Piemonte_. (Naples, 1897, 146 pp.) 6. ODDONE, E.--"I dati sismici della Liguria in rapporto alla frequenza ed alla periodicità." _Boll. della Soc. Sismol. Ital._, vol. ii., 1896, pp. 140-151. 7. OFFRET, A.--"Sur le tremblement de terre du 23 février 1887. Discussion des heures observés dans la zone épicentrale." Paris, _Acad. Sci., Compt. Rend._, vol. civ., 1887, pp. 1150-1153. 8. ----. "Tremblements de terre du 23 février 1887. Heures de l'arrivée des secousses en dehors de l'épicentre." _Ibid._, pp. 1238-1242. 9. ROSSI, M.S. DE.--"Relazione sui terremoti del febbraio 1887." _Bull. del Vulc. Ital._, anno xiv., 1887, pp. 5-17. 10. ----. "Bibliografia: Sul terremoto ligure del 23 febbraio 1887." _Ibid._, pp. 60-62, 107-112, 115-128.