1064 SPECIMENS OF
an irregular mosaic of calcite, the individual crystals of which measure about .04 to •o6 mm. in diameter, and minute granules or rhombohedra also of calcite, but measuring from .007 to .012 mm. in diameter.
Some small opaque cubes, rusty red by reflected light, are scattered here and there ; some are surrounded by a brownish halo. They appear to be oxidized pyrites.
On solution in hydrochloric acid an odour of petroleum is given off and a black dust of carbonaceous matter is left as a residue. On examining this under the microscope a small quantity of mineral matter is found to accompany it. The greater part consists of minute granules, many no more than .0087 mm. in diameter. They are colourless and transparent : some are found united in various ways, two combine to form a rod, or three or more are joined together and from these complexes crystals are built up, some with well-defined and continuous outlines, but hollow in the middle ; others, finally, are fully completed. forms. The specific gravity of this material was found to lie between 2.55 and 2.57, the refractive index a little above 1.5. One or two larger crystals measuring .04 by .o8 mm. were observed which closely resembled a common form of sanidine, and there can be no doubt that the whole of this material is orthoclase. The first impression produced when studying it is that it presents us with the various stages of growth from granules corn-parable with the globulites of Vogelsang up to the completed crystal, but on reflection another explanation appears to be possible ; the incomplete forms may not be the germs of crystals but the products of their dissolution, and this view is sustained by the presence of other minerals undoubtedly foreign to the rock, such as minute scales of muscovite and grains of quartz. This conclusion, if correct, has an obvious bearing on the supposed presence of primary albite in metamorphosed limestone.
Ta-shi-kou, Pei-shan. Epidole Rock.
A much-jointed fragment of an apple-green rock, containing obvious quartz.
The greater part of the rock is an aggregate of granular crystals of epidote ; it is traversed by numerous cracks running in various directions and now healed-up vein deposits. The rock has evidently been brecciated in place, but in addition movement has taken place along some of the fractures. Phacoids of another rock, retaining their original composition, are distributed along these fractures.
The phacoids consist of coarse quartz mosaics, showing undulose extinction, and large crystals of albite which are traversed by fractures and faults and otherwise deformed, as is shown by the curvature of the twinning planes and the production of secondary twinning which crosses the original.
Yeh-ma-ching, Pei-shan (oi—o6). Dolomite.
Fragments of pink compact dolomite traversed by veins of calcite and quartz and worn by the wind so that the quartz veins stand out in relief.
The rock is a very fine-grained aggregate of minute
ROCK AND SAND [Appendix O
crystals of colourless dolomite and granules of quartz, crossed by fine veins of quartz and calcite.
The granules of quartz when set free by solution are found to be coated with red oxide of iron, which dissolves with difficulty in nitro-hydrochloric acid.
3o. Yeh-ma-ching, Pei-shan (o7). Four miles S. of
Yeh-ma-ching. Grey Grit.
A light grey laminated grit composed chiefly of rounded and angular grains of quartz and sericitized felspar, with some muscovite and chlorite. Some of the quartz grains are composite and might have been derived from a granophyre.
Calcite is present, chiefly as a secondary constituent.
Yeh-ma•ching, Pei-shan (o8). Red Grit.
A fine-grained purple grit very similar to No. 3o. There is a noticeable quantity of fresh felspar, some of which is orthoclase, but the greater part albite or oligoclase. Iron ore is abundant and pyrites occur in small quantity. There is also a good deal of secondary calcite.
Pei-shan. Ridge flanking valley two miles NW. of C. 209 ; dip 82° SE., strike NE.—SW.
Fine-grained grit consisting chiefly of quartz ; there is a little felspar, some of which is andesine, also grains of calcite and needles of mica which are scattered throughout. The rock is traversed by thin veins of calcite, haematite, and quartz.
Pei-shan, C. 210 (o4). Amphibolite.
A compact non-foliated dark green rock.
This consists of a fine mosaic of quartz, through which are scattered in all directions long blades of green hornblende and flakes of brown biotite.
The hornblende extinguishes at 20° and is strongly pleochroic : X, pale straw colour ; Y, deep green ; Z, greyish blue. It is riddled with quartz, to which are also due its ragged margins.
The biotite, which is sometimes, but not always, intimately associated with the hornblende, is also strongly pleochroic : X, pale yellow ; Y and Z, deep brown. Some plagioclase felspar (andesine) contributes to the quartz mosaic.
Magnetite is fairly abundant ; apatite and zircons are also present, the latter surrounded by a pleochroic halo in the biotite which contains them.
Some thin veins of calcite traverse the rock.
Pei-shan, C. 212 (o6). Quartz Mica Schist.
A pebble of a compact greenish rock.
The greater part of the rock is formed by a mosaic of quartz with its components all elongated in one direction. Running parallel with them are flakes of muscovite and subordinate biotite, either as single crystals or in long trains.
The muscovite is closely connected with the biotite and in some cases can be traced into apparent continuity with it : thus a long transverse section of a muscovite cleavage lamella may be completed by biotite, and when the biotite is so orientated as to appear colourless no distinction can be discerned between the two parts of the section.
The biotite is strongly pleochroic : X, colourless to faint