8 10 THE JOURNAL OF GEOLOGY. 



walls, pointing to the fact that at the former place the eruption 

 ceased with the explosion which produced the crater ; a conclu- 

 sion strengthened by the absence of ashes and lapilli, with which 

 the crater and the upper part of the cone of Giorgio Kaimeni are 

 covered. 



Such then may be taken as the mode of formation of the 

 earliest and lowest portions of the two areas. As Reiss and 

 Stiibel have so well described, 1 we must consider the first erup- 

 tions to have formed a cluster of small islands in the sea near 

 the preexistent limestone islands, such as we find in the analo- 

 gous case of Santorini at the small Kaimeni Islands in the centre 

 of the bay. These earliest submarine eruptions and some of the 

 later ones took place either just before, or more probably during, 

 the later Tertiary period, 2 as is shown by the andesitic breccias 

 cemented by Neogene limestone. 



The analogy between Santorini and our region, however, 

 ceases with the formation of the smaller cumulo volcanoes, for 

 at the former place a large, thoroughly typical strato-volcano was 

 formed, while in the latter the later eruptions seem to have 

 belonged to a different type. These later eruptions were chiefly 

 subaerial and were continued into the following geological period, 

 and even, on Methana, into historical times. They were nearly 

 all eruptions of the dome (Kuppe) type — the exudation of 

 large masses of pasty material, accompanied by few explosions 

 and with little formation of tuff or scoriae, forming high steep 

 mountains or short thick streams. These eruptions did not take 

 place at one centre, but at various points of the region and along 

 fissures forming the complex of hills and mountains that we now 



see. 



That the main mass of both yEgina and Methana is made up 

 of such a complex of volcanic domes, and is not the denuded 

 wreck of a strato-volcano is clearly shown by the following facts : 

 The chief of these is the absence of inter-stratified beds of lava 

 and tuff, and of lava sheets, such as form the chief characteristic 



'R. &S.,p. 39- 



2 Cf. Neumayr. Geol. Bau. d. Insel Kos., etc. Denkschr. d. K. Akad. d. Wiss., Vol. 

 XL., 1880, p. 264; Philippson, Peloponnes., p. 433. 



