The P(ftrograp]iu of Om Fundamental Gneissose Complex. 45 



hornblende are poikilitic in structure, while in a few cases they retain 

 the ophitic structure which characterised the pyroxene from which they 

 have been derived. Not unfrequently, as in specimens from the Blue 

 Mountains and from the Mazaruni-Puruni district, the light-coloured 

 masses of hornblende- surround kernels of almost colourless pyroxene, 

 usually augite, but in some of the rocks from the Blue Mountains the 

 kernels consist of enstatite or of bronzite. In places the hornblende 

 has become actinolitic, and is frayed out towards its edges into minute 

 crystals of colourless amphibole, which in cases appear to run in 

 streams from and round the aggregates of the mineral. 



The feldspar is usually a more or less basic labradorite, which in 

 some specimens retains it crystalline form, the laths, however, being 

 more or less sericitised. More usually it occurs as either confused ill- 

 defined mosaics of clouded granules, or well-defined granular aggregates 

 of water-clear plates, the great majority of which are unstriated, whilst 

 some exhibit the stria? of plagioclase, or in a very few cases the 

 structure of microcline. Minute prisms of zoisite and of epidote are 

 frequently present in the feldspar, the former in places in some 

 abundance, the latter usually in very subordinate quantity, while 

 in some specimens the feldspar areas contain numerous minute needles 

 and hair-like fibres of colourless hornblende. Grains of secondary 

 quartz occur in addition to those of feldsj^ar in some of the 

 granular mosaics. Small irregularly shaped granules of titaniferous 

 iron are present in small quantity, and are usually coated with 

 leucoxene. In places the masses of hornblende contain many minute 

 grains of extruded secondary magnetite. In a few specimens small 

 iiakes of more or less chloritised biotite are present, but are only 

 sparsely distributed. A few small prisms of apatite occur in the rock, 

 and in some specimens minute crystals of zircon are found. Aggre- 

 gates of chlorite are present in many specimens, but, as far as I have 

 observed, this mineral seldom forms an important accessory. 



Actinolite- and Hornblende-schists. — In many places rocks occur, in 

 which the effects of metamorphism have been far greater than in the 

 epidiorites and amphibolites. These seldom contain any residuary 

 pyroxene, whilst the hornblende masses are either largely or entirely 

 broken up into actinolite, or into small allotriomorphic grains of green 

 hornblende. In places the hornblende masses are altered into more 

 or less fibrous aggregates of uralite. The rock has to a varying extent 

 a schistose structure, which in many places is not noticeable in hand- 

 specimens, although clearly seen in thin sections ; in other places the 

 rock has the well-marked chai'acteristics of a schist in hand-specimens 

 as well as in thin sections. 



The actinolite-schists vary in specific gravity from 2"89 to 2'94:, and 

 are made up of felted masses of pale-blue to almost colourless actinolite, 

 and of streams uf needles, and of long and narrow laths of the same 

 mineral, patches of chlorite, small irregularly shaped grains of titani- 

 ferous iron ore, and minute crystals of magnetite lying in a micromosaic 

 of feldspar with some quartz. In the mosaic the feldspar granules are 



