Geological researches in China, Mongolia, and Japan, during the years 1862-1865.

18 GEOLOGICAL RESEARCHES IN
The fuel, from this place, is almost all used in the tile-glazing establishments of
Peking.
Porphyries.-In the mountains north of the Wangping coal basin, the limestone
has been much disturbed by the intrusion of porphyry, which, in some places,
traverses it in the form of large dykes, and in others rising under it in large domelike masses, causes the overlying strata to dip from these in all directions.
As the porphyry conglomerates, at the bottom of the Coal series, are mostly
derived from these rocks, their eruption took place before the Coal measures were
deposited. Two varieties of felsitic porphyry were observed here, both younger
than the limestone, and both represented in the conglomerate. One of these forms
dykes on the ridge of Hiamaling and along the Hun Ho, between this ridge and
Chingpaikau. At the first-named place, it incloses immense fragments of the
black clay slate that divides the upper and lower members of the limestone.
This porphyry contains, in a compact, slightly greenish base, a little green mica
and numerous crystals of a triclinic, milky-white and slightly opalescent feldspar,
and is free from visible quartz. The feldspar weathers yellowish-red, and the base
dirty-white. The rock strikes fire with the steel, though not very readily.
Near Yenchi, on the Hun Ho, a few miles below Hiamaling, is the second variety.
It contains, in a light-pink base, crystals of feldspar, apparently orthoclase, and no
visible quartz. The porphyry that cuts off the coal rocks near the Tatsau, is probably younger than the Coal measures, although it is uncertain whether it occurs in
that locality as a dyke, or whether it is brought into the position it there occupies
by a great fault.
This rock has, in a compact gray base, tending to green, numerous prisms of
hornblende and small crystals of white feldspar, some of which at least are triclinic.
It contains no visible quartz, and strikes'fire with difficulty. Thus its characteristics are those of a hornblendic porphyry.
At Chingshui, two varieties of porphyry were observed, both traversing the coal
rocks. In one of these, the base is black and fine-grained, containing numerous
minute and small crystals of a transparent, colorless feldspar, certainly for the most
part triclinic. There is no visible quartz, and the rock strikes fire with difficulty.
About ten miles S. E. of the entrance to the Nankau pass, near the granite point
that juts out into the plain at Yangfang, there is an extensive fault in the limestone,
the strata of this rock dipping toward the fault. Between the line of this fault
and the granite there is a broad dyke of quartziferous porphyry. In a fine-grained
pink base, it contains crystals of pink orthoclase and abundant grains of quartz.
It may not be out of place to mention here the coal districts of Muntakau and
Fangshan. The former of these forms part of the Wangping basin where this disappears under the plain ot Peking. The valley of Muntakau form, in itself a
small bay, containing terraces of the plain deposit; there are said to be thirteen
seams of anthracite in the sides of the valley, most of which have been worked
since during the Ming dynasty.
Those seams which I visited alternate with sandstones and argillaceous shales,
and underlie the peculiar green quartzose conglomerate that characterizes the lower
part of the Chaitang series.