SKETCH OF sEGINA AND METHANA. 809 



the first submarine outpourings at any considerable depth the 

 conditions must be quite different, partly owing to the important 

 factor of the great pressure here involved. But when the lava mass 

 has reached nearly to, or a short distance above, the surface of 

 the sea we get a condition of affairs similar to that suggested by 

 Dana, resulting in the cooling and cracking of the lava stream 

 into solid blocks which are forced upward and onward by the 

 outpouring stream below, forming a cumulo volcano. That there 

 are few or no explosions during this phase of such a submarine 

 volcano may be accounted for by the action of the sea water in 

 cooling and condensing a large part of the imprisoned water 

 vapor, as well as by the presence of the numerous cracks in the 

 mass, serving as so many vents for its outlet. 



"Stone streams" 1 due to such a cause differ radically from 

 the ordinary lava streams made up of loose blocks, such as one 

 meets with on Vesuvius or Etna, which are due to a simple 

 mechanical breaking up of the solidified scoriaceous crust by the 

 movement of the mass and the frequent subsequent flowing away 

 of the liquid material. 



The eruption may cease at this stage, as at the May Islands 

 in Santorini ; or when a certain quantity of lava blocks has been 

 extruded, their mass and height above water varying with the 

 special conditions, the character of the eruption may change, as 

 at Giorgio Kaimeni, to the ordinary type, a crater being formed 

 and explosive ejections of ashes and lapilli, or the pouring out of 

 liquid lava, following. 



Now, to return to the Kaimeni of Methana, whoever has seen 

 the two volcanic masses produced by the eruptions of 1 866 at San- 

 torini and ca. 250 B. C, at Methana, cannot doubt for an instant 

 that the earlier eruption was of the same type as the later. We find 

 at Methana the same short high stream composed of a wild con- 

 fusion of angular lava blocks, with little scoria. There is also a 

 crater hollow at Methana, which however differs from that at 

 Giorgio Kaimeni 2 in being deeper and with more precipitous 



'JUNGHUHN: Java, II., p. 762. 



2 For plan of this crater cf. Fouque : Santorin., PI. XXX. and Ann. d. Sc. Geol 

 VII., PI. 7. 



