And what these layers -- that's what the surface used to be a million years ago, 10 million years ago, 100 million years ago, and you get deposits on top of them.
这些地层，就是一百万年前一千万年前或一亿年前的地表， 这些地层，就是一百万年前一千万年前或一亿年前的地表， 您可以从上面提取沉积物。