252 M. Kovanko’s General View of the Environs of Pekin. 
a considerable quantity of clay, and its beds have a thickness’ 
which is rather considerable. . 
The upper beds of this limestone have a great resemblance 
to that which forms such enormous masses in the Northern 
Mountains, and it is probable that they both belong to the 
same formation. 
The limestone of Mount Tzo-Tkhai, which is distinguished 
by the great pagoda situated on its flank, near the village of 
Shim-En-Gin, appears equally to belong to the carboniferous 
limestone. It is very compact, and the particles of quartz 
give it so great a degree of hardness as to strike fire with 
steel. Its texture is foliated, but in thick laminz. In some 
places it has the aspect of a compact mass. It abounds also 
in caverns, one of which, Thao-Yan-Doun, is remarkable for 
itS size. It is situated on a very steep slope, which renders it 
difficult of access. Many persons ascend the mountain on pur- 
pose to visit this cavern, but there are very few who have the 
courage to descend into it. Many absurd traditions exist 
among the Chinese respecting it. They pretend that there is 
a subterranean passage leading as far as Kafgane, and that 
there are stone-bridges over streams running through it, &e. 
&c. I made the descent into the cave out of curiosity. It 
appears like a steep gallery, at first tolerably high, but which 
becomes progressively lower, so as at last to render it neces- 
sary to crawl upon hands and knees. It terminates suddenly 
in a well ascending vertically. It was impossible to explore 
its farther direction, for at this point the burning wood which 
served me asa torch gave so little light, that I could scarcely 
distinguish the nearest objects. The air in the cave is very 
moist. There are two lateral galleries, one of which is under 
water; the other descends very rapidly, and is not any more 
accessible than the others. The cavern may be about 150 
sagenes in length. On the bottoms stalagmites are met with, 
but no organic remains, 
_ Coal Formation.—Slate-clay is largely developed to the east 
of Van-Pin-Koon. So much coal enters into its composition, 
that in some places it might serve for fuel. The beds often 
change their direction, and sometimes have a dip nearly ver- 
