STRATIGRAPHY OF THE MIDDLE YANG-TZI PROVINCE. 274 
SIN-T’AN SHALE. 
The Sin-t’an formation is prevailingly composed of olive-green argillite 
or massive shale, which is rather soft and frequently sandy, but not fissile. 
The sandy material occurs chiefly in the form of grains ranging up to the 
size of wheat, which are scattered rather than gathered in distinct layers. 
The lowest strata in the Sii-kia-pa region are black and brown clay-shales 
having a thickness of less than 100 feet. A typical massive green argillite 
follows, completing the formation with only slight variations. Near 
T’an-mu-shu-p’ing the uppermost layers are partly reddish mudstones. 
Again, 2 miles, 3.5 kilometers, above Ta-ning-hién, the upper horizon of 
the green argillites contains local thin strata of olive-green quartzite and 
earthy limestone. Just below Ta-miau-ssi the Sin-t’an formation contains 
not only green, but brown and gray argillites with thin coaly layers. This 
phase of the formation reappears in the main divide at the Ki-sin-ling and 
again in the vicinity of Chén-p’ing-hién. About halfway between the last 
two points, near Wa-tzi-p’ing, coaly layers are prominent, but no reliable 
report of the existence of workable coal in that vicinity was obtained. 
North of Ch6én-p’ing-hién metamorphism renders the formation more and 
more schistose and difficult to recognize. Besides the occurrences on the 
Ta-ning-ho and northward, the Sin-t’an appears along the Yang-tzi in the 
magnificent Wu-shan gorge, the I-chang gorge, and at Sin-t’an. The name 
of the last place has been adopted as a designation for the formation. 
The thickness of the Sin-t’an formation, as determined from the 
sections obtained on the Ta-ning-ho, is about 1,800 feet, 500 meters. 
In the transition with the underlying Ki-sin-ling (Sinian) limestone, 
the shale lies directly upon an even and unweathered surface of limestone 
as if in conformable relation. Where the limestone lies overturned upon 
the Sin-t’an, on the south side of the Ki-sin-ling, the transition between 
the formations was noted particularly, the layers of shale including seams 
of limestone which become more abundant and pass quickly into massive 
dark limestone with local shaly partings. Wherever observed, the contact 
with the overlying Wu-shan (Carboniferous) limestone presented an appear- 
ance of conformable bedding. Both upper and lower limits of the Sin-t’an 
are, therefore, regarded as conformable contacts. 
The green and variegated shales of the Sin-t’an have as yet yielded 
no fossils, but a small assemblage was obtained from a gray limestone 
which might be considered as occurring in the top of the Sin-t’an or at 
the base of the Wu-shan, in an exposure at the upper end of the chasm, 
immediately north of Tung-kuan-k’6u and south of Ta-miau-ssi (atlas 
sheet d 6). The fossils occur in granular greenish-gray siliceous limestone, 
