Travelling southward from Yii-lin Fu to Yen-an Fu we encountered 
Huang-t'u formation upon horizontal strata of sandstone and shale. The 
sandstone in places shows very marked bedding, and, owing to the deposition 
of mica between the layers, can be split without difficulty. This strongly- 
bedded sandstone occurs chiefly between Sui-té Chou and Ma-chia-k’ou. A 
good illustration of this may be seen in the photograph of icicles, taken about 
three miles south of Ch’ing-chien Hsien (Plate 17). The photograph shows 
too a typical source of the plentiful water-supply to be found in every ravine of 
North Shensi. 
At Yen-an Fu, the sandstone, still of a pale greenish colour, continues to 
show marked bedding. At low levelsa pink and green cross-bedded sandstone 
was noted. In the region of Yen-an, the sandstone contains many crystals of 
Iron Pyrites. These, of course, where exposed, are very much oxidised, but 
some fine unoxidised specimens were secured at Lao-shan. 
There is little to say about the Huang-t’u of this vicinity, except that 
at the ravine-bottoms it is inclined to be clayey, resembling Shao-t’u rather 
than loess. In the wooded area—which extends in a great belt, east and west, 
some twelve miles south of Yen-an Fu—there is an even greater predominance 
of Shao-t’u. Here also finely-laminated, dark blue-grey shale occurs just 
above the sandstone. 
Coal is mined at various places along the route from Yii-lin Fu to Yen-an 
Fu. Seams, reached by rather deep vertical shafts and showing no outcrops, 
occur within a mile of the former place. These mines produce a good- 
burning, but rather smoky, bituminous coal. At Sui-té Chou, a peculiar coal 
was secured: it was said to have been transported from Ning-hsia, on the 
western border of the Ordos. It is very heavy and dirty, but absolutely 
smokeless, and smoulders like charcoal. Once ignited, it will continue to 
burn with a dull glow till the mass is reduced to soft white ash. The substance 
is certainly not charcoal, and those who sold it said that it was mined like 
coal. It has neither the appearance, nor the lustre of graphite. At Ch’ing- 
chien a fine quality of lignite is obtainable. This comes from mines at An- 
ting Hsien, a town situated some twenty miles to the north-west of Ch’ing- 
chien. At Ma-chia-k’ou avery poor quality of coal occurs. This ignites 
only with the greatest difficulty, and leaves an enormous percentage of ash. 
Yen-ch’ang Hsien, a town situated about forty miles east of Yen-an Fu, 
is famous for its petroleum wells ; which are worked with European machinery, 
and produce a high grade of oil. We bought a supply of the oil, and found it 
burn well. It is sold at the rate of 23d. per catty (1 catty=14 lbs.) and finds 
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