142 PERIDOTITE. 



From Spur between Deadivood and Poker Flat, Cal. 



Ill P. A dark-yellowish and brownisb-green rock containing enstatite grains and 

 talc scales ; and traversed by ligbt-greenish serpentine veins. Section : a greenish-gray 

 mass flecked with magnetite grains and traversed by a grayish-3'ellow serpentine vein. 

 Tlie chief portion of the section is serpentinous material, in which besides the magne- 

 tite are scattered the remains of enstatite crystals and a few grains of olivine and diallage. 

 The serpentine varies in color from white to yellowish and green. In places clear white 

 leaves of talc associated with magnetite occur ; while some hematite is to be seen. Along 

 the sides of the serpentine vein before mentioned the section is black with the rejected 

 magnetite. Much of the enstatite contains the same inclusions that the brouzite variety 

 is accustomed to hold. 



The structure is shown in figures 3 and 6, Plate VI. 



Levanto, Italy. 



One specimen de.scribed by Prof. T. G. Bonney from this locality is a purplish- 

 or brownish-black rock veined occasionally with dull green, and flecked with crystal- 

 •line folia of glittering bronzite, while another specimen is of a more granular texture, 

 greener color, and rougher fracture than the preceding, but otherwise similar. The 

 second rock, in the thin section, is seen to consist chiefly of olivine grains separated by 

 threads of serpentine. It contains opacite, enstatite, augite, and perhaps a little diallage. 

 Opacite [magnetite] occurs in the enstatite and a little picotite was observed. 



The first specimen was seen under the microscope to have been completely altered, no 

 olivine remaining intact. Much opacite was found, which often forms continuous strings, 

 and is present to a greater or less extent in the grains that were formerly olivine. It 

 forms bands towards the exterior of the grains, or is disseminated throughout them. 

 Diallage and enstatite are both present, the latter being surrounded by a border of a ser- 

 pentinous mineral, into whicli are continued the principal cleavage planes, often marked 

 by opacite lines. Thin bands of serpentine indicate the prismatic cleavage.* 



Near Limni, Euhoea. 



A black splintery rock, whicli, as described by Becke, contains lustrous bronze-colored 

 grains of enstatite. Under the microscope it shows the evident maschenstruMur of the 

 serpentine which holds lens-formed masses of fresh olivine. This groundmass porphy- 

 ritically contains fresh enstatite of a pale brownish color and a marked fibrous texture. 

 This mineral is sometimes altered to a feeble bluish polarizing product. This alteration 

 extends from the exterior along the fissures towards the interior. Diallage, reddish- 

 brown octahedrons of picotite, and secondary magnetite also occur. 



Similar to this is a rock from Mantoudi, in the northern portion of Eubnea. This is 

 brownish, and contains numerous plates of enstatite in a fine-grained groundmass. No 

 diallage was observed, but the brownish color of the rock is due to brown hydrated 

 oxide of iron. 



Similar to this is a rock from the district of middle Euboea, between Chalcis and 

 Gides, which has a reddish-brown groundmass holding tombac-brown enstatite (bastite). 

 No olivine remains unaltered to serpentine. 



* Geol. Mag., 1879 (2), vi. 303-371. 



