Geologists have endeavoured to draw out the history of the terrible event which overwhelmed these islands and their inhabitants. At the beginning of the tertiary period, Greece, united to Africa, seems to have formed part of a large marshy continent, where now flows the Mediterranean. It was inhabited by those gigantic mammifers whose bones have been largely found in Africa. Towards the close of this epoch a lowering of the land separated Europe from Africa, and gave to the Mediterranean its present configuration. An oscillation of the crust of the earth afterwards produced openings, through which igneous matter has flowed. Torrents of lava gave birth to the volcanic rocks which are to be found in Greece and the neighbouring islands, and a volcano had evidently opened in the present bay of Santorini. The hill Saint Elias, the top of which forms the culminating point of the island, was then an island composed of schist and marble. The igneous matter, cooled by contact with the water and the atmosphere, attached itself to this hill, and the whole united together, formed the space now occupied by Santorini, Therasia, and Aspronisi. Repeated layers of lava, scoria, and ashes collected during many ages when the crater which occupied the central part was gradually becoming undermined. Volcanoes are the weak parts of the earth's crust; there is not one in full activity which does not present alternative series of increase or lessening. The cone rises gradually until by degrees it is obstructed with lava, then a sudden fall destroys it and hollows a new crater, sometimes larger and deeper than the first. Many such occurrences have been described, but none can equal in importance the gigantic fall which formed the Bay of Santorini. All the central part must have given way, and been suddenly ingulfed, leaving but a narrow border of land, through the northern part of which the sea has dashed to fill up the hollow. Instead of a mountain three thousand feet high, there is a bay of immense depth, surrounded by precipitous rocks, close to which ships can anchor. This violent catastrophe must have taken place when man was on the island; and the event must have been sudden, since the remains prove that there was no time to move away or to displace anything in the houses. The eruption of pumice-stone has preceded the sinking of the cone, for the tufa which covers the downs is cut through by subjacent streams of lava; nor does it seem to have been preceded by any violent earthquakes, as in that case the houses found in Therasia would have been demolished and the walls no longer standing. This is remarkable, as the construction of the buildings proves that the island was subject to them; the pieces of wood inserted in the walls seeming to be for no other object than to prevent the disastrous effects of such a shaking. This custom is still in use among all the islands of the Archipelago.