140 PERIDOTITE. 



The olivine is traversed by a network of dark -green serpentine fibres, and tlie diallage and 

 bronzite are both somewhat altered. Associated is a compact dark-green serpentine hold- 

 ino- some chysolite and chromite. Another rock from the same district is of a dark olive- 

 (••reen color, flecked with white spots ; and contains a platy greenish-brown shining diallage, 

 a deep green finely granular mass of olivine, and small white grains of anorthite. The 

 olivine is here traversed by a network of dark-green serpentine.* 



Fitchtelgehirge, Bavaria. 



These rocks are composed principally of olivine with enstatite, chromdiopside, augite, 

 and mao'netite. The olivine is more or less altered into a serpentine, showing the usual 

 network structure. The enstatite is in elongated, fibrous, brilliant clear wine-green 

 needles, and the chromdiopside in roundish, compact, somewhat fissured particles. The 

 groundmass consists of a mixture of chlorite, serpentine, etc.f 



A PchUe from the Jaina River, ten to twelve miles N. W. of Ml. Mariana, Chico, 

 Prov. San Domingo, San Domingo. 



252 G. A compact dark-green groundmass holding crystals of brownish pyroxene 

 and traversed by veins of chromite. 



Section : a gray groundmass holding iron ore and crystals of enstatite and diallage. 

 The groundmass is composed almost entirely of clear beautifully polarizing serpentine, 

 which shows in its structure traces of the bounding planes of the minerals from whose 

 alteration it was derived. A little white plagioclase, traversed by cleavage planes, was 

 ol)served, portions of which had been rendered gray and nearly opaque by kaolinization. 

 Only a few small fissured olivine grains were observed. The enstatite and diallage can 

 here as a rule be distinguished by their cleavage, the latter being much less regular than 

 the former, and closely like that of augite. Both are in irregular grains, more or less 

 altered to a greenish- and yellowish-brown product. Where the change lias progressed 

 far, the ordinary serpentine of the groundmass is the result. Sometimes the serpentine 

 resulting is filled with minute black globules, or with minute microlitic forms, ar- 

 ranged in lines forming definite angles with one another. The iron ore is in part in 

 crystals and part in irregular grains and masses. The structure is shown in figure 6, 

 Plate IV. 



This rock was collected by Professor W. M. Gabb. 



Starkenhach, Bhittenberg, Vbsges, France. 



According to Weigand this is soft black rock containing brownish-yellow and brass- 

 yellow crystals. In the thin section the rock is seen to be composed of bronzite (ensta- 

 tite), diallage, olivine, magnetite, hornblende (smaragdite ?), and picotite, with more or 

 less serpentine. The enstatite and olivine are more or less traversed by fissures filled 

 with serpentine. Tlie hornblende is in minute plates, while the bronzite is the predomi- 

 nating mineral.^: 



* Sitz. Wicn. Akad., 1807, Ivi. 201-274. 



f C. W. Giiinbel, Die paliiolitliisclien Eruptivgesteiue des Fichtelgebirges, 187^, l^p. 38-41. 



+ Mill. Mitth., 1875, pp. 192-190. 



1 



