ROCKS FROM NORTHERN AND CENTRAL CHINA. 439 
and iron oxides. In addition there are a few scattered bits of tourmaline, 
small quartz grains, and here and there a zircon, all of which are probably 
of clastic origin. The little tourmaline prisms are too ragged and worn to 
warrant the supposition that they are secondary crystals. The mass 
is thickly sprinkled with minute blackish flakes and formless shreds of 
carbonaceous material. 
This was formerly a siliceous shale in which slaty cleavage has been 
imperfectly developed. Most of the constituents appear to be those of the 
original mud, but the micaceous minerals and the quartz are probably in the 
early stages of recrystallization. 
Pyritic black slate, No. 109.—This is a local member of the partially 
metamorphosed Hei-shui system of the Ts’in-ling mountains, and was found 
exposed in the canyon below and above Siau-wang-tién. 
Specimen collected 2.25 miles, 3.6 kilometers, downstream from Chang- 
k’ou-shi, May 2, 1904. 
A dense steel-black rock through which are scattered numerous small 
bits and roundish bodies of pyrite (or marcasite) which range up to a centi- 
meter in diameter. ‘The cleavage is not as clean and even as it is in most 
slates, and the faces are therefore rough. 
In many ways the rock is comparable to No. 133, but represents a more 
advanced stage in the progress of anamorphism. ‘The crypto-crystalline 
ground-mass of quartz and graphitic matter contains abundant minute 
sericite flakes which have a distinctly parallel arrangement. 
Interspersed with this ground-mass there are a few bodies of pyrite 
inclosed sometimes in quartz, more frequently in zoisite, and sometimes in 
both. The areas are usually ellipsoidal and the outlines are ill-defined. 
In addition to these nodules the pyrite occurs as minute specks scattered 
through the rock. The zoisite also occurs separately in small irregular 
bodies or in larger nebulous clusters. The origin of these nodules is not 
evident at first sight, but the association of a lime-silicate with pyrite and 
organic matter, in a rock which may easily have been fossiliferous, suggests 
that the spots have been produced by changes induced by the presence 
of shell-bearing organisms in the original mud. The carbon and the sul- 
phur would be supplied by the decay of the organic matter, while the lime, 
iron, and alumina could be derived from the shells and the mud itself. 
RocKks OF IGNEOUS ORIGIN. 
Igneous rocks other than the Post-Carboniferous granites are rare in 
the Ts’in-ling district. In fact the only other intrusions noted are some 
small dikes of gray felsitic rock and schistose greenstone, which cut the 
supposed Pre-Cambrian schists and limestones at the mouth of the canyon 
of the Hei-shui-ho. Unfortunately we have no specimens of these rocks. 
