ROCKS FROM NORTHERN AND CENTRAL CHINA. 443 
parallel wisps of chlorite. In this dense ground-mass small lath-shaped 
prisms of pleochroic brown tourmaline, with an occasional zircon, are 
scattered without order. The zircons affect the schistosity of the mass 
as original sand-grains, but the tourmalines cut through the layers at all 
angles and without disturbing the micaceous bands; they are doubtless 
secondary minerals which have grown im situ. The abundant cloudy 
granules scattered about appear to be epidote and zoisite, which have 
probably arisen from alterations in the feldspars. 
The pebbles are of all sizes from several inches in diameter down to 
mere sand-grains. The majority are composed of quartz, but slate and 
bits of feldspar are also common. In addition there are bodies of calcite, 
some of which probably represent limestone pebbles; smaller bits of calcite 
occur among the products of decay of the feldspars. 
Under the microscope the pebbles show plainly the effects of the 
severe pressure to which the rock has been subjected. Many of the quartz 
bodies have been partly or wholly reduced to granular lenses around which 
the chlorite ground-mass bends. In case any of the original body remains, 
it is usually followed and preceded by granulated trails of quartz, forming 
the corners of the “‘eye-spots.’’ During the crushing the granulated quartz 
and the chloritic matrix have become intimately mingled, so that the edges 
of the pebbles have a frayed and ragged appearance. ‘The limestone frag- 
ments, if such they were, have completely recrystallized into coarse- 
grained calcite in which the cleavage and twinning planes, as well as the 
longer axes of the pebbles, lie at only moderate angles to the plane of 
schistosity. 
PSAMMITES. 
Green gneissic quartzite, No. 122.—The greenish gneiss is a phase of 
the schists referred to the Kui-chéu formation (Triassic?) in the canyon 
above Shi-ts’tian-hién. Specimen collected on the south bank of the Han 
river, at the sharp bend 2.5 miles, 4 kilometers, above Shi-ts’tian-hién. 
This is a light silvery-green rock, finely and evenly laminated, but with 
cleavage not well marked; there is a tendency to break across the laminz 
rather than parallel to them. The rock is very fine-grained, and the sur- 
face has a silvery sheen due to the presence of minute sericite flakes. The 
constituent minerals are largely of minutely granular quartz with some 
feldspar. The crystals are strained, as indicated by the undulatory ex- 
tinction between crossed nicols, and there is a notable parallel arrangement 
of the granules. At somewhat regular closely spaced intervals the highly 
quartzose bands are separated by others which are rich in sericite, chlorite, 
zoisite, and epidote, with a little biotite. The minute flakes of the micas 
lie with their axes roughly parallel, thus forming long seams and lamine. 
