University of California. 



[Vol. i. 



ing from the alteration of sediments by intruded igneous rock, stim- 

 ulated search for rocks showing the intermediate stages of meta- 

 morphism. As might be supposed, this effort met with more 

 success in the case of the smaller isolated masses of eruptive, and in 

 the areas west of the serpentine dyke, than in the main fourchite 

 sill, both from the fact that the metamorphic action did not proceed 

 so far, and that they have been better exposed through wave action. 



A piece of the sandstone, from near the contact with the intru- 

 sive rock of Point Blunt, was selected for examination. It does 

 not differ much in color and general appearance from the fresh un- 

 altered sandstone of Quarry Point. But close inspection, more 

 particularly of the weathered surface, shows that it has been pro- 

 foundly squeezed, and is somewhat veined with calcite. Under the 

 microscope it exhibits an ideal sheared structure imposed upon the 

 ordinary sandstone. The original clastic structure is still clear, and 

 fragments of black shale and eruptive rock can be plainly recog- 

 nized. But along the numerous shear planes, have been developed 

 delicate wisps of brightly polarizing white mica (muscovite). With 

 nicols crossed, it is seen that much of the original clastic material 

 has recrvstallized into a fine mosaic, composed probably of quartz 

 and feldspar, ami the formerly rounded grains have taken on fantas- 

 tic corroded forms. Fine needles of blue amphibole are quite 

 abundant, generally clustered into pale blue or lilac-colored aggre- 

 gates. Zoisite is fairly abundant in small prismatic individuals with- 

 out distinct terminations. They often have a conspicuous trans- 

 verse parting. It is colorless, with a high index of refraction and 

 consequently strong relief. The double refraction is very weak. 

 The extinction is in every case parallel with the prism and the 

 interference figure biaxial. The habit in general is very similar to 

 that of the zoisite in the fourchite groundmass. Some long jointed 

 prisms also occur, however, resembling closely those figured by 

 Becker.* 



Glaucophane in irregularly bounded crystals and bundles of 

 fibers was also found in other places near the contact with the 

 fourchite, in sandstone which macroscopically appears but little 

 altered. 



■■Quicksilver Deposits of the Pacific Slope. Monog. XIII, U. S. G. S., p. 

 78, Fig- 1, d. 



