AMPHTBOLITRs AND RELATED R< Kfi III I \\ II I 273 



A typical lioinUende-lcIs is \<i. ;>|s. a Muck, heavy, massive rock. It is fairly 



se-grained, and in the hand specimen appears to consist wholly of hornblende. 



In section, it is composed chiefly of fresh green hornMende, containing a few inclusions 



of rounded quart/ blebs. Quart/ is the more important minor constituent, and there 



in addition, accessory flakes of l>iotite. grains of felspar, calcite, apatite, and 



ilmenitc. 



Specimen No. 950 is a biotite-hornblende-schist . \\liich is closely related to 

 the biotite-amphibolites. It contains felspar and a little quart/, but in less amount 

 than in the typical amphibolites. The brown biotite is abundant, but not uniformly 

 distributed through the rock. It forms clusters, in which some of the micaceous 

 laminae are bent and twisted. Occasional grains of epidote are associated with the 

 biotite. Green hornblende is the most abundant constituent, and both the hornblende 

 and biotite possess pleochroic haloes, which surround minute inclusions. 



A curious hornl)lende-fels is No. 941. It is a dark-green, massive rock with a 

 porphyroblastir appearance, due to platy crystals of hornblende, which are set in a 

 fine matrix. The examination reveals the large hornblendes as relic crystals which 

 have for the most part broken down into granulitic aggregates of a similar pale-green 

 hornblende (PI. XL, fig. 3). The latter forms the bulk of the thin section. A little 

 colourless chlorite and a little brown biotite are mixed with the granulitic hornblende. 

 Embedded in these aggregates are a few long, slender prisms with ragged terminations, 

 which are feebly pleochroic from colourless to pale green. Some show lamellar 

 twinning, and they possess straight extinction with yellow and grey polarisation colours 

 of the first order. They show cleavage, and appear to be a form of orthorhombic 

 amphibole. The remaining constituents are ilmenite dust, and grains of pyrite and 

 apatite. It would appear as if the original platy hornblende had been chloritised and 

 the reaction had then been reversed, reproducing the fine granulitic hornblende from 

 the chlorite. 



Another dense hornblende-schist is No. 209, in which a subordinate amount of 

 liiotite, for the most part converted into chlorite, is associated with the pale bluish 

 green, granular hornblende. It contains large talcose areas, similar to those in No. 513, 

 produced by the decomposition of pre-existing olivine or pyroxene. These areas form 

 about half of the section, and contain magnetite in a similar manner. They are 

 studded with inclusions of hornblende and chlorite, but there is no trace of the 

 original mineral. 



The family of actinolite-scnists is represented by specimen No. % J4<5, which 

 displays in the hand specimen a bright green mass of acicular crystals. Its appearance 

 forms a distinct contrast to that of the dark greenish black hornblende-schists. In 

 thin section it consists almost entirely of a mass of long thin a-tinolite prisms, which 

 are pale green to colourless. A few flakes ot biotite and a few scattered grains of 

 ilmenite are the only other minerals present. 



