44 



University of California. 



[Vol. i. 



and amygdaloidal habit, and the prevalence of glass in the ground- 

 mass show that portions at least of the masses here described are 

 surface lava flows. That the whole of the carmeloi'te exhibited in 

 the different areas is of the character of a lava flow cannot be posi- 

 tively affirmed. Indeed, there is evidence that not only have we 

 the lava as extruded in approximately horizontal sheets at the sur- 

 face, but also that a portion of one of the masses occupies a position 

 in the vent from which the surface flows emanated. Thus on the 

 northwest side of Sunium Point there is a vertical plane of contact 

 between the carmeloi'te and the conglomerates of the Carmelo series. 



A careful inspection of this contact shows clearly that the 

 carmeloi'te is eruptive through the conglomerate, portions of the 

 latter being inclosed in the igneous rock. Thus it would appear 

 that the mass of carmeloi'te which occupies the extremity of Sunium 

 Point is of the nature of a volcanic plug. In direct continuity with 

 the mass are rocks on the shore east of Sunium Point, which have 

 intercalated agglomerates and are thinly laminated; they also show 

 flow contortion and vesicular and amygdaloidal structure, with the 

 amygdules flattened in the planes of flow, the latter being at low 

 angles with the horizon, dipping seaward. These are undoubtedly 

 surface lavas. Comparing the plug rock with the surface flow in this 

 and the other areas, an interesting fact comes out. The plug rock of 

 Sunium Point is the only facies of this volcanic formation in which 

 phenocrysts of augite are present. In the plug rock these augites 

 abound; in the surface lavas they have not been observed. The 

 glass is not so abundant in the plug rock as in the surface flows, 

 and it differs from the latter, also, in having very numerous globulites 

 present in the ground-mass. As regards the chemical relations of 

 the two facies, only two analyses of carmeloi'te have been made. 

 One of these, however, is of the plug rock, and the other of a sur- 

 face flow at the lagoon area, and results are of much interest (see 

 analyses, pp. 38,42). The plug rock contains only 52.83 per cent of 

 silica, and has a specific gravity of 2.80, while the surface flow con- 

 tains 60 per cent of silica, and has a specific gravity of 2.51 to 2.54. 



The intrusion of the conglomerates of the Carmelo series by the 

 carmeloi'te at Sunium Point establishes the age of the latter as cer- 

 tainly later than that series. Both the plug facies and the lava 



