THE TERRESTRIAL PERIDOTITES. — PICRITE. 151 



all possible colors from a pale apple-green to a brilliant grass-green, bright ochre-yellow, 

 siskiu-green, and reddish-brown, one color running into the others. Further, there occur 

 remnants of the olivine grains having a light or ochre-yellow tinge, and also magnetite 

 and gothite. The olivine remnants when untouched by alteration are colorless, very 

 pellucid, beautifully polarizing, but extraordinarily rich in fissures, whose edges are cloudy 

 •with minute magnetite grains. Some show a light blue color, owing to exceedingly 

 minute powder-like grains. Vapor, glass, and fluid cavities, as well as spinel inclusions, 

 occur sparingly. 



The serpentine mass includes fiery reddish-bi-own mica ; very light grayish-brown, 

 finely fibrous, or step-like, rough, feebly dichroic enstatite ; a little clear light-brown, 

 feebly dichroic augite, traversed by irregular fissiires ; and sti-ongly dichroic fissured horn- 

 blende, varying from clear ochre-yellow to a deep blackish-bruwn. A little apatite and 

 plagioclase were also observed. This is a cretaceous or tertiary eruptive rock.* 



Pcn-y-carnisiog, Anglesey. 



According to Bonney this rock in the section is seen to be composed of augite, horn- 

 blende, actinolite, magnetite, opacite, serpentinous material, etc. 



Augite occurs in colorless grains and crystals, some of which show a characteristic 

 cleavage. Tlie hornblende, including actinolite, is in (1st) innumerable small acicular or 

 blade-like crystals, in irregular tufted group.?, which are pale greenish or colorless, and 

 feebly, if at all, dichroic; (2d) small crystals often exhibiting cliaracteristic cleavages and 

 even crystallographic planes, green-colored and strongly dichroic ; and large brown crys- 

 tals, supposed to he pseudomorphs after augite. These minerals occur in a serpentinous 

 or chloritic groundmass containing no unchanged olivines, but pseudomorphs after that 

 mineral were thought to be observed. Some talc (?) was seen, as well as otlier micaceous 

 secondary products.-f . 



Later Professor Bonney found a number of boulders of this rock on the western coast 

 of Anglesey. In general these were similar to the one just described, although in one 

 some decomposed feldspar and some diallage were observed. A little apatite, mica, etc. 

 were seen in some of the sections. J 



Near the River Dill {^^ DiUgegend"), Nassau. 



This rock in the fresh condition has a blackish-green color, and contains copper-col- 

 ored mica, green chromdiopside, hj^perstheue, picotite, and magnetite. 



The olivine is in water-clear to pale yellowish-green grains, traversed by fissures 

 along which occurs a fibrous greenish or yellowish-green serpentine containing mag- 

 netite grains, etc. The chromdiopside appears as a rule in irregular leek-green grains 

 showing cleavage, and is sometimes altered to a leek or smaragdite-green serpentinous 

 aggregate. 



The hypersthene is pale-brownish, aTid sliows an evident brachypinicoidal cleavage. 

 It contains the usual violet-brown laminre, and olivine grains. 



The mica shows a reddish-brown color darker than tlie hypersthene, is dichroic, and 

 associated with the magnetite. The picotite is in deep Vilack octahedral crystals, which 

 are dark brown, and feelily translucent on the thin edges. 



* Neues Jahr. Min., 1875, pp. 700-703. f Quart. Jour. C4col. Soc, ISSl, xxxvii. 137-110. 



% Quart. Jour. Geul. Soc, 18S3, xxxis, 254-260. 



