Fairbanks.] 



Geology of Point Sal. 



73 



termed contemporaneous segregations, which, on account of a pro- 

 longed period of solidification, took on their coarsely crystalline 

 character, and the other true dikes of later age than the rocks which 

 they intersect. It is not always possible, however, to draw the line 

 between them. The segregated veins in the gabbro do not differ 

 much, or even any, from the average composition of that rock. 

 They consist of feldspar, diallage, and olivine. The two former in 

 large individuals, the last in aggregates of grains as in the normal 

 rock. Veins of essentially the same composition appear also in the 

 peridotite, but in the hypersthene area there are very coarse vein- 

 like masses of hypersthene and feldspar which do not appear else- 

 where. 



Veins with black hornblende appear at one spot west of Point 

 Morrito. It is associated with feldspar and augite. The augite in 

 a pure granular aggregate forms the outer portion of the vein, 

 while in the center are feldspar and large crystals of hornblende. 

 A fragment in which the cleavage was well developed was examined 

 with a goniometer and the angle found to be the same as that of 

 normal hornblende, namely, 124 30'. 



The altered dunite and related rocks east of the Chute are inter- 

 sected by many slender veins contrasting strongly in color. They 

 consist of diallage and a white substance which under the micro- 

 scope is generally completely isotropic. From its close resemblance 

 to the feldspars of the olivine rich rocks which are undergoing a 

 change to a similar cloudy milky substance, it is believed that it 

 belongs among the feldspars. The veins vary in width from half an 

 inch to two inches. In the narrower ones the pale green diallage 

 is confined to the outer edge. The crystals seem to be planted on 

 the walls and to have grown inwards. The center consists wholly 

 of the dull feldspar. In the wider veins the pyroxene is not con- 

 fined to the edge, but is scattered throughout indiscriminately. 



At the foot of the cliffs south of the Lion's Head some large 

 pieces of serpentine were found which are cut by white dikes or 

 veins four to five inches wide. The substance of which they are 

 composed is fresh and clear, and contains long, slender, brownish 

 crystals sparingly disseminated along the edges. The walls of the 

 dike are clean cut, with no transition to serpentine. Slides prepared 



