. Bulletin of the Department of Geology of the University of California. Ransoms Eruptive Rocks of Point Bonita. 85. Figure 6.—Radial grouping of plagioclases in spheroidal basalt at B. x 35. Secondary alteration is here also well advanced, and the plag- ioclases do not lend themselves to accurate measurements of The few readings obtainable gave extinction angles of about 170, indicating labradorite. THE DIABASE. Occurrence.—As may be seen by turning to the map, this rock occurs in the southern portion of the area, as a narrow, dyke-like band, traversing the spheroidal basalt, the relative pos
. Bulletin of the Department of Geology of the University of California. Ransoms Eruptive Rocks of Point Bonita. 85. Figure 6.—Radial grouping of plagioclases in spheroidal basalt at B. x 35. Secondary alteration is here also well advanced, and the plag- ioclases do not lend themselves to accurate measurements of The few readings obtainable gave extinction angles of about 170, indicating labradorite. THE DIABASE. Occurrence.—As may be seen by turning to the map, this rock occurs in the southern portion of the area, as a narrow, dyke-like band, traversing the spheroidal basalt, the relative positions of the two near the lighthouse being shown in the accompanying section, B' B". As the cliff is here one hundred feet high, and practically vertical, it was not possible to make a close inspection of the east- ern contact, but, looking down from above, it appears to be very irregular, and the pyroclastic rock seems to have been ruptured and displaced. There can be little room for error in regarding it as a true igneous contact, for faulting could hardly have taken place along so irregular a surface without the production of considerable friction- breccia, of which there is here no trace, On the north side of the toe-like projection, upon which the lighthouse stands, the pyroclas- tic rock does not appear, and the diabase can be traced by the eye, as a rather indistinct band alone the face of the Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original University of California, Berkeley. Dept. of Geology. Berkeley : The University
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