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University of California. 



[Vol. i. 



times polished, and have a greasy feel, like talc. The rock varies in 

 color from a dirty white to a peculiar bluish-green tint. Traversing 

 the rock in places are veins of chrysotile, the silky fibers at right 

 angles to the walls, and bands of marmolite of various shades of 

 green and blue. These sometimes alternate in parallel layers, and 

 more rarely change from one to the other. Minute faults may be 

 seen in these veins, giving evidence of movement of the rock after 

 their formation. Threads of magnetite penetrate the serpentine, 

 and the slickensides are in places incrusted with small octahedral 

 crystals of that mineral. In one locality a vein of earthy magnesite 

 occurs; at its point of greatest thickness it is about six inches across, 

 but divides into smaller veins and then thins out. It cuts the ser- 

 pentine almost horizontally, extending along the face of a street 

 cutting for a length of about seventy-five feet. Chalcedony occurs 

 in a few places as a coating on the serpentine or in veinlets. 



On large exposed surfaces of this facies of the serpentine there 

 frequently appear spheroidal masses, sometimes very numerous, of 

 diameters ranging from six inches to three or more feet, separated 

 from one another by bands of the crushed and slickensided material. 

 These masses give the rock almost the effect of a boulder con- 

 glomerate. The interstitial serpentine is crushed and drawn out 

 around the spheroids, having the appearance of a plastic cement 

 moulded to them. On examination, these spheroidal masses are 

 found to be portions of the original rock mass, which have escaped 

 the shearing and complete decomposition to which the rest of the 

 rock has been subjected, their roundefl forms being due to the 

 wearing away of the angular portions by repeated movements of 

 the surrounding rock in every direction. The character of the 

 rock composing these spheroids will be described in detail under 

 the heading of the "massive facies." 



In certain limited areas the serpentine has escaped the general 

 crushing action. In such places it appears as a typical massive 

 serpentine, dark green in color, translucent on thin edges, with sub- 

 resinous luster and splintery to conchoidal fracture. In some 

 specimens no other mineral is present except small crystals of 

 chromite and magnetite. More commonly there are scattered 

 crystals of enstatite imbedded in the massive serpentine, noticeable 



