198 RESEARCH IN CHINA. 
THE PLAIN OF PEKING. 
To the unaided eye the Plain of Peking appears to be a monotonous 
level, in which artificial elevations are conspicuous because natural ones 
are wanting. Instrumental observations show that there are considerable 
differences of level between widely separated points, but the slope by 
which they are connected is so slight as to be inappreciable. Streams in 
their natural channels are rarely sunk a yard below the surface of the 
plain, which frequently descends slightly in a direction away from their 
immediate banks. 
Hills which rise above the plain are of three classes—those which are 
the tops of partly buried mountains, those which are dunes of drifting sand, 
and those which are artificial Among the latter is to be classed the 
so-called Coal Hill, in the Imperial City, according to the testimony of 
the most reliable observers. 
The level of the plain extends, with remarkable uniformity, almost 
and sometimes quite to the base of the mountains, but wherever a ravine 
or valley opens onto it the surface is raised by deposits of gravel and sand 
from the mountain stream. These deposits constitute an alluvial cone, 
as it is called, which merges into the general imperceptible slope of the 
plain. Where many small ravines lie near together, their alluvial cones 
become continuous and constitute a belt. The head of an alluvial cone 
may lie high upon the mountain side, and in some instances such a one 
has been chosen as the site of a monumental tomb. That of Ch’1-yu-f6n, 
20 miles northwest of Peking, is a striking instance; the Ming Tombs 
are in part similarly situated. 
It will be noted that the Plain of Peking is the surface of that earthy, 
sandy, and gravelly material which fills the embayment in the mountains. 
The constitution and arrangement of this material is of fundamental im- 
portance in the question of underground waters which may be reached 
by a deep well, and it has been made the object of such observation as is 
possible without boring. At Peking the surface, so far as can be seen, is 
composed of fine silt and sand. It has been worked over in the gradual 
growth and decay of the city or cities during ages, until its original condition 
and arrangement are lost. It is stated on good authority that foundations 
of old houses are found 25 feet below the present level. Three miles west , 
of the west gate of the Chinese city, on the road to Lu-k’ou-kiau, very 
coarse gravel, mingled with fine sand, begins and is continuous thence to 
the Hun. This gravel is plainly the material distributed by the Hun in its 
latest excursions over the plain, together with dune sand and dust blown 
from other areas. 
