THE TERRESTRIAL PERIDOTITES. — DUNITE. 121 



Dun Moimiain, Neiv Zealand. 



The peridotite (dunite) of Xew Zealand is described by Hochstetter as a Mesozoic 

 eruptive mass, associated with serpentiue and hyperite, also of eruptive origin. This 

 dunite is a crystalline-granular rock, of light yellowish-greeu to a grayish-greeu color on 

 the fresh fracture, and weathering to a dirty, rusty, sometimes yellowish, sometimes red- 

 dish-brown color. Fracture uneven, granular, angular, and coarse-splintery. It was 

 found to be composed of granular olivine, holding octahedrons of chromite, with rounded 

 edges. The serpentiue was formed by the alteration of the peridotite in situ* 



M. Eeuard lias given a brief description of the microscopic characters of this rock. 

 The section is composed of irregular grains of olivine, but of larger size than those in 

 the St. Paul's peridotite, to be described later. " With this exception, the other uiicro- 

 sco[)ical characters are the same in both rocks : the fissures, more or less regular, marked 

 by black lines, intense chromatic polarization of the olivine, roughness of the surface, 

 etc., etc. The sections of chromic iron in dunite are larger tlian those in the specimens 

 from St. Paul, but in other respects they present the same features." f 



Somhnore, Norvmy. 



The thin sections of this rock, according to Brogger, contain predominating olivine, with 

 (very sparingly) beautiful green smaragdite, here and there a grain of brownish-} ellow 

 enstatite, and chromite in little grains. The olivine is fresh, clear-green, and in the sec- 

 tion colorless, and fine-granular. Some grains show one cleavage parallel to the longer 

 direction of the crystals, and anotlier perpendicular to the same. Only a trace of altera- 

 tion to serpentine was observed. The smaragdite is of a green color, fresh, and shows 

 pleoehroism. The only two grains in the section were elongated in the direction of the 

 vertical a.xis, and sliow cleavage lines running in the same direction. The enstatite 

 occurs in a few scattered grains. Tliey are fresh, brownisli-yellow, finely striated, and 

 crossed by cleavage-planes. The chromite appears in little, irregular, rounded grains. 



This peridotite is associated with and lying in schists, and is called by Brogger an 

 olivine-schist. % 



Rohergi'ik, SJcrenakkcn, Noma)/. 



This rock was described by H. von Mohl as composed principally of olivine grains, 

 containing octahedrons of picotite and deep hair-brown, transparent, chromite crystals. 

 Magnetite was present, and some of the olivine grains showed a change to fibrous chry- 

 sotile. Lamella; of fibrous enstatite were seen. § 



Bonhoinmc, Blnttenherg, Vosf/cs, France. 



A blackish-green rock, with a rough, splintery fracture, showing a brilliant shimmer 

 from numberless minute points, and traversed in part by many blackish veins. In thin 

 splinters it is clear-green and translucent. In the section the olivine grains are seen to 



* Zeit. Deut. geol. Gcsell, 1S6I-, xvi. Sil-o-il; Rcise tier Novara, Geologic voii Ncu-Seeland, pp. 217- 

 220. 



f Report Challenger Expedition, Narrative ii. Appendix B. pp. 22, 23. 

 X Neues Jahr. Min., ISSO, ii. 1S7-192. 

 § Nyt Mag., 1877, xxiii. lli. 



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