Like many parts of the world, China is geologically
a geological
assemblage. North China is one block, and some of the oldest rocks in
the world are to be found there. South China, or, more precisely,
central and southern China—forms another block, itself the product of a
geological merger. But these elements had become part of what is now
Eurasia well before the breakup of Pangea into Laurasia and Gondwana,
so that in this sense China, unlike the southern Near East or India, is
an original part of Laurasia. It has nevertheless been strongly
affected by the junction with India through the uplifting of the
Tibetan plateau, which it also adjoins. The fact that both regions have
aboundary with Tibet means that they have a number of features in
common.
A first comparison concerns boundaries. India is pretty
well delimited
by the combination of mountains to the north and ocean to the south. In
the case of China mountains do indeed mark the limit of the region to
the west, and ocean does the same to the southeast and east (though the
oceanic frontier is much more sensitive to changes in sea level than in
the Indian case, with the result that China is much larger in an ice
age). But this still leaves China with two significant land frontiers
that are not blocked by high mountains. One of these frontiers is in
the southwest, where China adjoins Southeast Asia; this is the shorter
of the two, and movement across it is impeded by jungle. The other is
the long northern frontier, which runs through open country. It is this
frontier that has mattered most to Chinese history in terms of both
threat and opportunity—the threat of conquest by nomads from the
steppes to the north, and the opportunity for contact with other
civilizations to the west.
Another comparison concerns the distribution of mountains
and plains.
Like India, China has its highlands, though again they are unimpressive
in comparison to those of Tibet. But whereas India has a single block
of highlands in the south and a single concentration of alluvial plains
in the north, the makeup of China is more complex: as one moves from
north to south, river valleys alternate with bands of highland terrain.
Much as in India, it is two rivers rising from the Tibetan plateau that
dominate the picture; but here both flow from west to east. North China
is the land of the Yellow River. In the northwest it flows through
massive windblown deposits of a yellowish soil known as loess (hence
the name of the river). Farther east it picks an unstable course
through a vast accumulation of silt that it has itself transported from
the loess deposits upstream. Central China is dominated by the Yangtze,
which has likewise created an extended alluvial plain. Both rivers are
dangerous, but their valleys—especially that of the Yangtze—have
remarkable agricultural potential. The highlands that separate the two
are a residue of the joining of the two main blocks out of which China
was formed. South of the Yangtze, China is not lacking in rivers with
agriculturally exploitable valleys, but none are on the same scale.
