4 2 



University of California. 



[Vol. •>. 



At the extreme end of the Point the dikes of dark structureless 

 lava become more numerous and on the south side give place to 

 banded or sheeted varieties of varying color. Brecciated dikes of 

 the dark aphanitic basalt are numerous. These are in part perhaps 

 friction breccias, and in part have apparently resulted from the break- 

 ing up of partly consolidated flows. The sheeted rocks are cut by 

 dikes of diabase possessing a coarser, more granular aspect. They 

 are bunchy and broken and often terminate in breccias, the dike con- 

 tinuing to grow narrower until it disappears, when its place is taken 

 for a number of yards by the broken rock of the fissure walls. A 

 highly scoriaceous body of dark lava has been forced up through the 

 sheeted rock in places, and above the reach of the waves it weath- 

 ers out in fantastic cavernous forms. It is often brecciated and 

 filled with epidote. Adjoining one of these bodies is a dike of 

 greatly decomposed but coarsely crystallized rock containing boul- 

 ders of an amygdaloidal lava. This lava is somewhat similar to that 

 of the volcanic neck a little to the east, and may be continuous 

 with it. 



About a quarter of a mile east of the end of the Point, and oppo- 

 site the seal rocks, a much coarser rock than any yet observed 

 makes its appearance in the cliffs. It cuts diagonally across the 

 sheeting of the basalt which runs parallel to the long diameter of 

 the mountain. The dikes cutting the sheeted lavas have a diabasic 

 structure, while this large body of coarsely crystalline rock which 

 forms the coast line for some distance opposite the seal rocks 

 is a gabbro. It forms the cliffs for perhaps 1,000 feet, and, 

 although slightly finer grained on its edges, presents a fairly uniform 

 character. It is finally displaced again along the upper part of the 

 cliffs by the banded basalt. The latter has an exceedingly gnarled, 

 ragged character, with contorted bands and scoriaceous texture. 

 The cavities are generally empty and sometimes three inches long, 

 while they are twisted in all sorts of shapes. Many dikes, some of 

 them not over three or four inches in thickness, have been intruded 

 in the gabbro near its edges. They vary in color from greenish to 

 almost jet black. The larger ones have a granular diabasic charac- 

 ter, while the smaller are aphanitic. Banded or sheeted rocks, simi- 

 lar to those west of the gabbro, replace it toward the east, cutting 



