alluvial clay strongly impregnated with alkali, through which run deep caiions : 
an especially large one occuring to the east of Hui-ning Hsien (Plate 38). 
As Hsiao-shui-tzti is approached, a system of high mountains makes its 
appearance tothe south and south-west. From these mountains thestreams bring 
down great quantities of pebbles and boulders of limestone and crystalline rocks, 
At Hsiao-shui-tzi (or Shao-shui-tzii) itself the Yellow River is again 
reached, at this point cutting through a thick dyke of granite to a depth of 
200 feet (Plate 33). On this granite lies a layer of green sandstone and on 
this again a deep deposit of loess. The loess here seems to contain a certain 
amount of whitish clay, and becomes extremely hard under the influence of 
the hot sun. 
The formations round Lan-chou Fu are very complex. There is a good 
deal of felspathic rock, especially north of the river, which here flows through 
a long valley, from two to three miles wide. 
To the south of the city, sedimentary rocks are first encountered, but 
these give way to crystalline rocks, which rise to a height of from 10,000 to 
11,000 feet. Westward, the mountains to all appearance are formed of igneous 
rocks, and very complicated. Gold, silver-ore, jade and precious stones are 
obtained in this range. 
The sedimentary strata, which occur some ten miles south of Lan-chou 
Fu, namely at Wa-kang-ch’éng, are coal bearing ; whilst a plentiful supply of 
clay—derived probably by decomposition from igneous rocks—allows of 
extensive pottery-works being carried on. 
There is a good deal of grey crystalline limestone in the mountains south 
of the city. These are more or less rounded, no very prominent peaks existing. 
Loess occurs at an altitude of over 7000 feet. 
The next stretch of country to be discussed is that along the road taken 
by the Expedition on its return journey from Sui-té Chou, in North Shensi, 
eastward to Fén-chou Fu, in Shansi, and thence north-eastward to T’ai-ytian 
Fu. Between Sui-té and the Yellow River very deep deposits of loess and 
Shao-t'u occur. The latter is found usually at the bottoms of the deep ravines 
and is of a deep brick-red colour. In places the ravine-bottoms are formed of 
the usual sedimentary strata (Shensi formation) with marked horizontal 
bedding. Within five miles of the Yellow River the loess gets very shallow, 
and in many places the sandstone substrata are exposed in the form of rounded 
hills with precipitous ravines. The depth (500 to 600 feet), to which the river 
has cut through the sedimentary formation, is much greater here than at the 
spot further north where the Expedition crossed on its journey westward. 
126 
