When the water reaches the more resistant bed of limestone 当水流遇到更坚硬的石灰岩床时

52. In Borneo, rain has sculptured the limestone into extremely sharp-sided pinnacles.
    在婆罗洲 雨水已将石灰岩 雕凿成无比尖削的石塔
53. But the dissolving power of rainwater has other, much more dramatic effects underground.
    不过在地下 雨水的溶解作用 还能产生其它更壮观的效果
54. Rivers that flow over limestone often seem to completely disappear.
    流经石灰岩的河川 到最后似乎总是无影无踪
55. When the water reaches the more resistant bed of limestone
    当水流遇到更坚硬的石灰岩床时
56. its course is altered.
    就会改变路线
57. Once underground,
    一旦进入地下
58. the water takes on a new, more erosive power.
    水便有了一股新的、更强的侵蚀力

来自《行星地球 第一季 第四集 Planet Earth S01E04 洞穴》第 55 行