8 12 THE JOURNAL OF GEOLOGY. 



production of domes. Being porphyritic andesites and dacites 

 of medium to rather high acidity they were, when ejected, in a 

 pasty rather than a very fluid condition, — the state of viscosity 

 which is essential to the production of domes and masses of great 

 height as compared with their lateral extensions. 



Another fact in favor of the view here held is the total absence 

 of dikes, which are rare in dome eruptions, but common and 

 characteristic in those of the other type. This might, perhaps, 

 be explained by the small amount of denudation, inasmuch as 

 dikes, when present, are much more numerous and of larger size 

 near the base than in the upper layers of volcanoes of whatever 

 type. 1 Their total absence, however, cannot reasonably be so 

 explained and, taken in connection with the facts above men- 

 tioned, must be regarded as a confirmation of the present view. 

 It may be added that the columnar structure of Mt. Stavro 

 and the laminated structure of Mts. Oros and Chondos, which 

 are characteristic of Kuppen, point in the same direction. 



It is probable, however, that in some places, streams of more 

 liquid lava were poured out, as east of Mt. Stavro, and perhaps in 

 some of the ridges to the south and east of Mt. Oros, which I was 

 unable to examine. As has already been suggested, there also 

 may have been true craters on Methana, though it does not appear 

 probable to me. These, however, would be secondary phenom- 

 ena, and we must regard it as certain that the great majority of 

 the eruptions which formed the two regions were of the dome 

 type, as defined by von Lubach, 2 based on a substructure of 

 cumulo-volcanoes, which have also been formed in some of the 

 later flanking secondary eruptions. 3 



Relative age of the various lavas. — It has already been briefly 

 noted, and we shall see at greater length later on, that lavas 

 of quite diverse chemical and mineralogical composition were 



1 Cf. Geikie, Text-Book of Geology, 1893, p. 233. 



2 Z. d. d. Geol., Gesell. XVIII., 644. 



3 It is noteworthy that the eruptions of andesites, very similar to those described 

 in this paper, which occurred at Milos (according to Ehrenberg) and at Smyrna, 

 Sipylos and Pergamon (according to my own observations) were all decidedly of the 

 domal type. 



