1849.] LYELL ON THE STRUCTURE OF VOLCANOS. 219 



separates it from the New Kaimeni is in one part 100 fathoms deep. 

 The two other summits spoken of are submerged cones, one occur- 

 ring on the north and the other on the east of the Kaimenis, the north- 

 ern peak being twenty-four fathoms underwater and 1158 feet high, 

 the eastern peak twenty fathoms, giving it a height of 1 25 1 feet above 

 the bottom of the crater. Their summits are flat. They spring from 

 the same ridge as the Kaimenis, and the whole mountain with its five 

 summits nearly bisects the gulf in a north-east and south-west direc- 

 tion, a direction not assigned to the Kaimenis in maps published pre- 

 viously to the late survey (see Map, fig. 4. p. 216). 



From a history of the successive formation of different parts of 

 this central volcano, or volcanic ridge, we derive the knowledge of 

 facts of great geological importance, for we are taught that the Kai- 

 menis owe their present elevation not only to the heaping up of cones 

 of fragmentary matter, but to the bodily though partial upheaval of 

 portions of the trachytic mass, bearing on its surface a thin layer of 

 pumiceous ash, containing marine shells. The rise of this bed of 

 pumice, first called the White Island, in the year 1/07, is on record, 

 and it has been examined of late years by Mr. Edward Forbes, who 

 made a collection of the marine shells contained in it, among which 

 were both univalves and bivalves, of the genera Pectunculus, Area, 

 Cardita, Trochus, and many others, all recent species of the Mediter- 

 ranean *, in a fine state of preservation, and implying that the sea- 

 bottom on which they lived, when enveloped by a fall of ashes, was 

 between twenty and thirty-five fathoms in depth. The state of the 

 bivalves, their shells double with their valves closed, with the epi- 

 dermis remaining, indicated that they had been suddenly destroyed. 

 We know therefore from the habits of these mollusca, as observed by 

 Mr. Forbes in the Mediterranean, that an upheaval of at least 220 

 feet was required to bring them up to the level of the sea, above which 

 they now rise to the height of five or six feet. This bodily upheaval 

 of a certain mass of ashes does not appear to have affected the other 

 two islands equally, if at all, at the same period, still less to have ex- 

 tended to the outer islands ; for if so, such ports as Phira, built on 

 the water's edge, on a talus of fallen fragments from the vertical cliff, 

 woidd have been carried upwards. We have here then an indispu- 

 table proof, in the Gulf of Santorin, that in the gradual reconstruc- 

 tion of a volcanic mountain in what was previously the original centre 

 of eruption, large masses of solid matter may be lifted up in mass, 

 150 or 200 feet, and sustained at that height, while other parts of 

 the volcano in the immediate vicinity do not participate in the move- 

 ment. This power of the lava or gases to carry upwards, to a height 

 of 200 feet or more, a stratified deposit, which M. Virlet considered 

 as having floated like cork on the top of a denser fluid, is a phaeno- 

 menon which may perhaps aid us in comprehending how, in some 

 steep isolated hills, like the Puy Chopine in Auvergne, the volcanic 

 mass may have been uplifted, together with large fragments of the 

 granite on which it reposed, as MM. von Buch, Le Coq, and Dau- 

 beny have held. We learn that when the new island Neokaimeni 

 * British Association Report for 1843. 



