Millions of years of water action has dissolved the limestone rock, forming a system of flooded caves and tunnels.

数百万年的水流运动溶解了石灰岩，形成了积水溶洞和隧道。

So if they’re exposed to acidic rain, or flowing water, some water can seep below the surface and erode the rock, forming a hidden underground cavern.

因此， 如果它们暴露在酸雨或流水中， 一些水会渗入地表以下并侵蚀岩石，形成一个隐藏的地下洞穴。

Then they rolled down a pass, the chocolate-toned rocks forming a wall on both sides, from one of which fell a heavy jagged shade over half the roadway.

然后他们滚下一条通道，巧克力色的岩石在两侧形成一堵墙，从其中一堵墙中，一大片参差不齐的阴影覆盖了一半的道路。