154 PEKIDOTITE. 



shows to some extent tlie characters of serpentine replacing olivine. The dark band is 

 formed of irregular masses and grains of iron ore, arranged in the serpentine in a vein-like 

 form. Some of the serpentinous material is isotropic. The structure of a portion of the 

 section is shown in figure 1, Plate VI. 



At the foot of the first rise on the ridge, edge of the river on the road from. La Vega 

 to Jarahacoa, Province of La Vega, San Domingo. 



142 G. A dark reddish-brown compact rock, breaking with a conchoidal fracture. 

 Traversed by some veins of a greenish-white serpentine. Contains many bronze-like 

 crystals of altered enstatite (?). (W. M. Gabb, Collector.) 



Section : a brownish and greenish mass composed of serpentine, dolomite, picotite or 

 chromite, and ferrite products. The usual arrangement of the serpentine, in a network 

 following the outlines and fissures of the original olivine grains, is seen ; this is marked 

 by veins formed by brown and black dust and grains of ferruginous material mixed with 

 serpentines, having a similar arrangement to that observed in the California peridotites. 

 Bordering these veins is a band of whitish serpentine, which sometimes occupies the 

 entire interspace. In the majority of cases the portions between the veinlets are com- 

 posed of a greenish-yellow sei'pentine having the form and outline of the fractured 

 olivine grains. 



Lying in the sections are a number of white, greenish, and grayish patches, of the same 

 outline as the pyroxene minerals usually occurring in the peridotites. They enclose 

 rounded portions of the serpentinized olivine ; and in part have the fibrous cleavage of 

 enstatite, while in part their structure is irregular. They show aggregate and fibrous 

 polarization as a rule, but occasionally the optical characters of altered enstatite. Pico- 

 tite or chromite occurs in irregular masses of a black and translucent deep coffee-brown 

 color. Its grains are traversed by fissures and black bands, part of which, in reflected 

 light, show metallic lustre with numerous crystalline facets. 



Some dolomite with well-marked cleavage occupies a portion of one section, in the 

 form of irregular somewhat rounded patches. A few veins traverse the mass, having been 

 formed after the main serpentinous alteration of the rock. The wdiole section is sprinkled 

 with black-brown and yellowish-brown grains, dust, and aggregations of ferruginous 

 material. The structure of this rock is shown in Plate V. figure 4. 



Brixlegg, Tyrol. 



According to Von Drasche this shows a compact network of magnetic iron grains, with 

 a fibrous serpentine mass, which encloses some remaining grains of olivine and diallage. 

 The serpentine is said beyond question to have resulted from the alteration of olivine antl 

 diallage.* 



II Piano, Elba. 



A greenish-brown mass traversed by talcose (?) veins, and containing altered enstatite 

 cry.stals. 



Under the microscope it is seen to be composed of brownish, greenish, and yellowish 

 serpentine largely filled with black dust-like granules, having a network structure and 



* Mill. Mitth., 1S71, i. 2. Sec also E. Tlussak, Ibid., 1S82 (2), v. 76, 77, who found aiigilc in this 

 rook, and ilirows sonic donbt. on tlie correctness of Drasche's work. 



