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

8 GEOLOGICAL RESEARCHES IN
and this is the case with all the exposed sections from the outlet to the Siauku shan
or Little Orphan rock. Below Tungliu coarse red sandstone is exposed, its upturned
edges, which are here capped with the younger terrace deposits, trending to N. E.
with a dip of 15~ to N. W. At Nanking there are extensive quarries of limestone,
while directly opposite the city, on the left bank of the Yangtse, strata of red sandstone trend W. S. W., dipping about 40~ to E. S. E. Coal mines are worked in
the immediate neighborhood of this city, especially on its eastern side. Soon after
leaving the hills of Nanking the river enters the great delta plain through which it
winds to the sea.
In a resurne I shall try, by means of a combination of the data given above, with
information derived chiefly from native sources, to throw more light on the structure
of this region.
TERRACES OF THE YANGTSE VALLEY.
At frequently recurring points along both the Upper and Lower Yangtse, we
meet with deposits of gravel and clay, forming bluffs at the water's edge, or fringing
the hills that form the walls of the valley. They are generally stratified in
horizontal beds. Differing in height and in the character of their ingredients, there
seems also to be a diversity of age. The extensive plain, once occupied by the
Tungting lake, before it was reduced to its present size, is fringed by these terraces;
for they recur constantly from Hankau to Yochau on the right bank of the river,
and from this city along the eastern border of the lake, and form a belt which
extends many miles to the south, and occupies nearly all the space along the southern edge of the lake, between the Siang and Yuen rivers. Again, where the river
enters the lake plain, the tongue of land included by the river bend between Pahyang and Tung'sz, consists of the same deposit.
At the last named locality the deposit is made up of rounded pebbles of quartz
and limestone, cemented with a stiff clay, and this is its general character at the
junction of the Siang river with the lake and along the eastern shore. But the
most general form of occurrence is that of a stiff blue clay, with irregular white
spots. Near Tung'sz the terraces appear to be from seventy to ninety feet high,
but below the outlet of the lake they vary from thirty to sixty feet. Blackiston
mentions similar terraces as occurring at various points along the Yangtse in
Sz'chuen.
The village of Tsingtan, at the eastern end of the Mitan gorge in Western Hupeh,
is built on a terrace of conglomerate-breccia formed of fragments of limestone,
chert, gneiss, and other metamorphic rocks, in form of rubble and rounded and
angular fragments of all sizes, the whole firmly cemented by a calcareous tufa.
This formation originally filled the valley from side to side, and its bluffs rise forty
to fifty feet above high-water mark. In the rapid current that must always have
scoured these narrow portions of the Yangtse valley, nothing but the coarsest
material could resist the onward movement; and when an increase in the velocity
of the stream took place, only those portions of the deposits were preserved which