ransome. j Eruptive Rocks of Point Bonita, Hi 



fering in the possession of a pronounced flow structure, and in hav- 



Figure 4. — Section of spheroidal basalt from the interior of one of the bales 

 shown in PI. 7, Fig. r, with a portion of one of the dense green 

 amygdules. x 21. 



ing a general fresher appearance (Fig. 4). The feldspars have 

 arranged themselves tangentially about the amygdules, and where 

 two of the latter lie close together, the feldspars between all lie with 

 their longer dimensions parallel. Several curved crystals were also 

 noted. The amygdules are nearly round, from 1 to 4 mm. in diam- 

 eter, dark green in color, and almost opaque. They are made up 

 of a felt of very fine needles, with one or more central spots, filled 

 with clear quartz, into which the delicate needles penetrate singly 

 and in little tufted aggregates. With No. 7 Hartnack the needles 

 are seen to be pleochroic, being light green parallel to their length, 

 and colorless at right angles to it. The extinction is approximately 

 parallel. They are suggestive of actinolite, but are too minute for 

 certain identification. A few opaque grains, presumably magnetite, 

 are also present in the slide. 



The rock forming the spheroidal masses at the head of the land- 

 ing stairs (Fig. 1) is dark gray in color, compact in texture, and 



* 



