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

CHINA, MONGOLIA, AND JAPAN. 23
another enlargement of the Yang Ho valley, and are also lake terrace deposits. The
road lies over this lake bed till about ten miles N. E. of the city of Siuenhwa (fu),
where a spur extends westward from the mountains. This spur consists of a double
ridge, with an intervening longitudinal depression, the southernmost portion being
formed by beds, highly inclined to N. and trending E. W., of quartzite, red argillaceous sandstone, and a compact white rock, apparently an altered argillite. These
beds, which seem to be the equivalent of the great limestone formation, will be
referred to again in discussing the Hwaingan strata.
The northern part of the double ridge is a remarkable porphyry, which has either
traversed or overlies the last mentioned beds. This rock may be called the Kalgan1
porphyry, as it is extensively developed around that city, although it occurs also in
the hills of the Gobi desert. It belongs to the trachytic series.
On the southern flank of this spur the lake deposit rises rapidly toward the hills,
and the firm loam, of which it here consists, is cut into by deep gullies. In one of
these places a section is exposed of horizontal beds, apparently the tufas of the
/l]]][]" i I Fig.7 l l7 l' i I' I!I I, li
Ilia ali |^^^^ ^
a. Terrace loam. b. White tufa. c. Red tufaceous sandstone.
Kalgan porphyry. The effects of an erosion previous to the deposition of the lake
loam are visible.
We shall find similar tufaceous deposits intimately associated with the Kalgan
porphyry near that town.
From the spur we have been examining we follow the road over the lake deposit,
to Kalgan, or Changkiakau. High and rugged hills of the trachytic porphyry
inclose the valley on the east, while to the north lies a higher range of mountains,
which, as it forms a geographical as well as political boundary, and represents
approximately the line of the Great Wall, we may call the Barrier range.
a. White and red tufas. b. Kalgan porphyry. c. Tower of the Great Wall.
At Kalgan this range is traversed by a gorge, with vertical walls, through which
a small stream finds its way to the Yang Ho from the edge of the Mongolian plateau.
1 The Russian name for Changkiakan, an important market town and gate of the Great Wall.