200 RESEARCH IN CHINA. 
During this subsidence the sea and the rivers have been in constant 
conflict, the sea ever seeking to spread over the sinking land, the rivers 
ever bringing down sediment to build out the land. The delta of the 
Mississippi or the Nile or the Huang-ho illustrates the work of the rivers. 
The subsidence and the filling-in have progressed gradually. ‘There 
has been abundant time for the work of subsidiary activities on the surface 
of the filling, and we may thus conceive of the material beneath the present 
plain as having been spread and redistributed by streams and winds, as 
we now see it spread and distributed. At any particular stage of the 
process, at any level, there was coarse gravel near the hills and resting on 
bed-rock; there was sand along its inner margin, and the central area of 
the plain was composed of irregular stretches of sand and fine silt or clay. 
A drill-hole sunk through this deposit should pass through many 
layers of clay, sand, and gravel of various textures and mixtures. Some 
may be small in area and isolated; others may be very extensive and con- 
nected with strata at much higher levels. The lowest, next to bed-rock, 
is probably the most extensive, as it must underlie the whole plain; the 
most open because it consists of the coarsest materials; and the one reaching 
to the highest levels, since it extends up onto the present mountain slopes. 
Water may be found in any of the sandy layers. An artesian flow 
is most likely to be secured from the deepest. 
Data for estimating the depth of filling of the Bay of Peking are 
meager, but not altogether lacking. The depression is recognized as a 
sunken valley, sculptured by running water. There are many examples 
of similar character and of like magnitude in the neighboring province of 
Shan-tung, and some of these have not been so filled as to hide the floor 
of the valley. The valley of the upper W6n-ho, near Lai-wu, east of T’ai- 
an-fu, is many miles across, is nearly flat over considerable areas, and is 
diversified and bounded by mountains which rise abruptly from it. The 
bed-rock is widely exposed. Reasoning from this comparison, we may 
infer that the slopes of the mountains about the Bay of Peking descend 
to a depth, which is probably not excessive, beneath the plain, and are 
connected by a comparatively flat floor. The fact that so large an area 
as the Bay of Peking has been filled by streams, which though of con- 
siderable size are not great rivers, is an argument in favor of compara- 
tively moderate depth. At Peking it may be 1,000 feet from the surface 
to bed-rock; it probably is not 2,000 feet. 
THE WATERS OF PEKING. 
A small stream, the Tung-mi, enters the city from the northwest, 
feeds the canals and lakes in the Imperial City, and flows away through 
the Chinese city to the Pei river. It has no value as a source of water. 
Wells are numerous in Peking. Some of the principal ones in use by the 
