f 



78 University of California. [Vol.*. 



present shape under the influence of gravity. A certain amount of 

 crushed and sheared material fills the interstices between the sphe- 

 roids, and seems to be made up of comminuted fragments of the 

 same rock. It is, however, too crumbling and too full of second- 

 ary products for a satisfactory determination. The rock of these 

 spheroids has a pronounced porphyritic texture,— the crystals of 

 feldspar varying from those of small dimensions up to those of 

 about 15 mm. in length, and standing out conspicuously on the 

 weathered surface as light-colored spots. The mass shown in the 

 illustration was drilled and split open, but the interior showed no 

 perceptible difference, either in structure or texture, from the exte- 

 rior surface, and was traversed by irregular joint planes. < 



Upon descending the steep talus -slope to the strip of beach 

 to the west of the spheroidal masses, the contact can be made out 

 between the spheroidal basalt and the diabase; the latter appears to 

 be intrusive, and includes, near the contact, a few of the character- 

 istic rounded forms of the basalt. At the southern end of the beach 

 the peculiar spheroidal structure is very conspicuously shown. The 

 forms are here lenticular, rather than spherical, as may be seen from 

 the large detached masses, three to five feet in diameter, newly 

 fallen from the cliff. The rock has been minutely fractured in an 

 astonishing manner, and in places is a mere mass of brittle fragments, 

 slightly recemented together. The spheroidal structure is also 

 exhibited at the northern end of the beach, where the rock is exces- 

 sively shattered, and filled with veins and stringers of calcite. On 

 the way down to the beach, and within a few feet from the top of 

 the slope, a block of sandstone about four feet in diameter was 

 observed resting partly imbedded in the volcanic rock. 



The spheroidal basalt may again be closely examined, along the 

 beach northwest of the old tower, but presents no new features. 

 From this beach northward, the cliffs are inaccessible until the low 

 land at the stream mouth is reached. The position occupied by the 

 spheroidal basalt at F, is represented somewhat diagrammatically in 

 Fig. 3. The portion shown on the left of the sketch forms a low, 

 wave-washed projection, with smooth, water-worn surfaces, show- 

 ing very conspicuously the structural peculiarity which is so char- 

 acteristic of this rock. It is evident that the mass is not a homo- 



