SINO-MONGOLIAN FRONTIER 
exposing the archaic formations beneath. On 
the north-western side of the range the strata 
flatten out and probably continue horizontally 
up to and beyond the Yellow River. I did not 
notice any sign of the Hu-t’o series, but doubtless 
they exist. 
North-east from Wu-chia-kou the geology of 
the country immediately adjoining the Ning- 
wu Fu district, as already stated in my geological 
notes in Through Shén-Kan, shows a series of 
shale and sandstone ridges (Shansi formation), 
the strata of which dip to the east at angles 
varying from 30° to 80°. The ridges are formed 
by escarpments on the west and dip slopes on 
the east. It is in some of the higher and more 
gentle hollows, caused by this configuration, 
that lie the fresh-water lakes, mentioned in 
Chapter II of this book as having been newly 
discovered in January of 1910. 
Here again the Shansi formation is replaced 
westward by the Ki-ch’ou formation (limestone), 
the strata of which dip to the east at very sharp 
angles. The outcrop of archaic rock, which has 
extended unbroken north-east from the Wu- 
chia-kou district, has tapered down, disappear- 
ing altogether before Ning-wu Fu is reached. 
267 
