6. China
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.