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THE YELLOW LANDS. 191
On the plateaux encircled by mountain barriers forming closed basins the
yellow earth forms a uniform layer of unknown depth. But wherever the erosive
action of running waters has had full play, enormous fissures with vertical walls
have been opened in the argillaceous mass. The water, penetrating rapidly
through the countless empty spaces left by the roots of plants, gradually disinte-
grates the soil, breaking it up into perpendicular blocks. The more exposed
masses, giving way, form irregular cliffs, broken up in all directions, and creating a
labyrinth of deep gorges flanked by perpendicular walls. In some places the work
of erosion has left little beyond mere terraces, or isolated eminences, often
resembling feudal strongholds. Elsewhere the gradual infiltration has excavated
underground galleries in many districts affording shelter for the whole population.
The erosions reveal in some places a thickness of at least 2,000 feet, offering a
prodigious quantity of fertilising soil constantly washed down, and maintaining the
productiveness of the plains watered by the Hoang-ho. For this yellow earth is the
richest soil in China, being far more fertile even than ordinary alluvium. It
requires no manuring, and goes on producing heavy crops for ages without
showing any signs of exhaustion. It contains all the nutritive elements of plants,
while its porous character is such that the moisture penetrates far into the soil,
returning by capillary attraction, charged
with all the chemical substances in
solution which contribute most to the alimentation of the vegetable growths. It
even serves as a manure for other lands, over which it is distributed in large
quantities. Such is its efficacy that it enables the peasantry in the cold regions of
North China to raise crops of cereals at an elevation of 6,500 feet, and in some places
even 8,000 feet, whereas in the warmer provinces of the south the land is seldom
cultivated beyond 2,000 feet above sea-level.
Much ingenuity has been displayed in overcoming the difficulties offered to free
communication by the perpendicular walls of the yellow lands. To pass from river
basin to river basin advantage has been taken of every narrow fissure, deep cuttings
have been made in many places, and fresh routes opened when these have been
filled up by the landslips. Some of the most-frequented roads have been
excavated to depths of from 40 to 100 feet and upwards, and the labour expended
on all these works is at least equal to that lavished on the building of the Great
Wall, or the construction of the Grand Canal. The roads are sometimes continued
for -hundreds of miles almost in the bowels of the earth, but are seldom more than
8 or 10 feet wide, the wheeled traffic being conducted by means of shuntings like
the " gares " in the Suez Canal. In dry weather the waggons sink into the dust
up to the axle, while after the rains the tracks are converted into quagmires,
dangerous alike to man and beast. Yet these difficult highways, being quite
unavoidable, possess great strategic importance, the blockade of one of these defiles
at a single point being often sufficient to cut off all communication between
extensive regions.
The mountains whose lower slopes arc covered by the yellow earth also contain
some of the richest coal beds in the world. Anthracite arid other varieties are
found in all the provinces watered by tributaries of the Hoang-ho Pechili,