122 PERIDOTITE. 



be clear and fresli, but in some points a change to serpentine has taken place. Picotite 

 and a reddish garnet (?) were observed. 



The other accessories were a few plates of amphibole minerals and iron ores.* 



KarUt'dtten, Austria. 



Tschermak describes a grayish-green, fine-grained rock from this locality, as com- 

 posed of olivine, united with serpentine, grass-green smaragdite, and little, black, pitch- 

 like, or semimetallic grains of picotite.f 



Tron, Oesterthal, Norivay. 



This is similar to the serpentine from the Andestad See to be later described. The 

 olivine grains are changed, along their boundaries and fissures, into a chrysotile. This is 

 in part of a platy-granular structure, and part composed of parallel fibres. In some por- 

 tions grains of olivine with unaltered centres are to be seen. Considerable magnetite 

 was observed. 



Enstatite is comparatively rare, and when present contains some picotite grains and 

 crystals, a few of which were seen in the olivine. J 



A section of this rock obtained from K. Fuess is entirely altered to serpentine. The 

 gray, serpentine groundmass is traversed by bands of ferruginous and gray material, 

 resembling closely those represented in figures 1, 2, and 4 of Plate V. Dark-brown, trans- 

 lucent picotites were observed scattered through the serpentine, their borders jagged and 

 opaque, probably as a result of alteration. The serpentine is filled with minute black 

 grains of some iron ore. 



Heiersdorf., Saxon?/. 



According to Dathe, the Heiersdorf rock is medium grained, containing pale-red gar- 

 nets, and showing under a lens quartz and feldspar, with light-greenish and brownish 

 olivine, as well as black, lustrous crystals. The principal portion of the section is olivine. 

 This is seldom fresh, but generally cloudy or altered to serpentine, forming the usual net- 

 work, and containing some dust-like ore. The olivine contains some picotite or chromite 

 grains. 



Plates of magnesian mica occur in the neighborhood of the garnet and ore particles. 

 The garnets are of the size of a pin's head, and are somewhat altered. The majority are 

 entirely changed from the singly-refracting garnet substance to a doubly-refracting, radi- 

 ately-fibrous material. This has a pale-blue aggregate polarization color, but in common 

 light is greenish and feebly dichroic. The minority of the garnets have a small alteration 

 zone surrounding them, of colorless fibres, probably asbestus, arranged perpendicular to 

 the garnet boundary. Light-brownish zircon grains also occur. § 



Honda Mountains, Spain. 



The serpentine of the Ptonda Mountains, covering an area of nearly 600 square miles 

 has been described as eruptive by Joseph Macpherson.|| With the serpentine were 



* 13nmo Weigaiid. Mill. Mitth., 1875, pp. 186-193. 



t Sitz. Wicn. Akad., 1807, hi. 275-279. 



t Njt, Mag., 1877, xxiii. 120, 121. 



§ Ncucs Jahr. Min., 1876, pp. 227-229. 



II On the Origin of tlie serp;nitiue of tlie Ronda Mountains, J. Macplierson, Madrid, 1876, 20 pp. 2 plates. 



