40 



University of California. 



[Vol. i. 



substance, as if alteration were proceeding by a discharge of the 

 iron oxide. This greenish substance is in part, at least, secondary, 

 and different in its optical behavior from the green varieties of the 

 iddingsite; it is probably serpentine. 



In some of the slides the phenocrysts of plagioclase are much 

 larger than those in the rock of the Sunium Point area, and in others 

 phenocrysts of this mineral are absent. The difference may be due 

 to the fact of specimens having been taken from different flows, but 

 whether this was the case or not could not be recognized in the field. 

 In those cases where there are large phenocrysts of plagioclase, the 

 latter are frequently charged heavily with inclusions which resemble 

 closely the finer portions of the ground-mass in the immediate vicin- 

 ity of the phenocryst. Sometimes this included matter is arranged 

 peripherally, while in other cases it is central, or is evenly distributed 

 throughout the entire section of the phenocryst. A little chalcedony 

 was detected in some of the slides; but this, together with quartz, is 

 abundant in the form of amygdules in the amygdaloidal facies of the 

 rock. 



In the ground-mass of these sections, also, there is in addition 

 to the magnetite a considerable amount of minute granules of a 

 deep brownish red translucent mineral (limonite). The iddingsite 

 of the ground-mass is usually greenish yellow in color, and occurs 

 in shred-like patches devoid of crystallographic boundaries. It 

 lies between the plagioclases in the ground-mass, and does not 

 exceed the latter in size. It seems to bear an ophitic relation to the 

 plagioclase. It is distinctly pleochroic, has parallel extinction, low 

 refractive index, strong double refraction, and otherwise resembles the 

 paler varieties of the phenocrysts of the same mineral. 



The Abalone Point Area. — On the north side of Abalone Point 

 there is an area of perhaps ten acres of carmeloi'te, abutting against 

 the granite on the one side, and passing beneath the terrace forma- 

 tions and blown sand on the other. The rock is often much decom- 

 posed, appearing as a purplish red, earthy mass in which the origi- 

 nal character of the formation can be recognized only with great 

 difficulty. The fresher portions present at least two distinct facies. 

 One of these is a dense bluish rock with irregularly parallel streaks 

 of greenish yellow through it. The other is nearly uniformly of a 



