Nothing is stopping the magma from seeping even deeper into the sandy subsoil.

没有东西可以防止岩浆继续向下渗透到沙质底土。

It is an ancient city and its subsoil is packed with ancient remains.

伦敦是一座历的城市，因此城市的底土都埋藏着先人的遗骨。

Do you know why the soil is so much darker in colour than the subsoil and the rock beneath it?

你知道吗, 土壤的颜色为什比底土及其下方的岩石多?

At one time the soil was just like the subsoil, and before that it formed part of some hard and solid rock.

曾几何时, 土壤与底土一样结实, 再往前追溯的话, 它还曾经是坚硬、结实的岩石。

In some places the workmen may have to dig down only a few feet before they reach the rock, but in other places both the soil and the subsoil may be many feet deep.

有时候, 工人们可能只需挖掘几英尺便能看到岩石层；不过另外一些时候, 岩石层上方的土壤与底土可能达到很多英尺之厚。

So rock fragments from the subsoil can end up concentrated on the surface.

因此, 来自底土的岩石碎片最终会集中在表面。