Yulong Cave and the water under Pengshui

Pengshui's own geographers describe the county as two mountains holding one trough, and the phrase is a description of soluble rock. The Wu River and its Yu tributary cross the county in a V, the ridges stand close on both sides, and the seat at 245 metres is only the floor of the trench. Three named peaks rise above a thousand metres, Qiliangzi at 1,434, Baila at 1,393 and Fenghuang at 1,048, and above them the highest ground reaches 1,859.6. The cave is one of the places where that height is returned to the river: a passage in the limestone that carries water down instead of over.

A cave is a record of water losing its load. Rain takes carbon dioxide from the air and from the soil, becomes a weak acid, and dissolves calcium carbonate from the limestone on its way down. Where the water reaches an air space and releases the gas, it drops the lime again: a straw from the roof, a sheet down the wall, a rim around a pool. The shapes are arithmetic rather than decoration, a balance between the rate of the drip and the amount of lime in it. That is why the same cave looks different in different chambers, and why a dry chamber is a chamber where the water has found another way.

The cave is called Yulong, Jade Dragon, which is the sort of name these places are given and tells you nothing about the passage. Its value is local before it is scenic. Pengshui is a county of 3,903 square kilometres, 54.2 per cent forest and 59.5 per cent minority, with 545,094 people at the 2010 census and a tourist list built on the Wu River gallery and the Ayi River. A cave enters that list as a place to shelter from the rain, to sell a ticket and to keep a road open, and the water that made it is the water the valley lives on.