Aquifers don't form *above* a specific type of soil, but rather within it.

Here's why:

* Aquifers are underground layers of rock or sediment that hold groundwater.

* These layers need to be permeable, meaning water can easily flow through them.

* The type of soil or rock determines the permeability. Some soils, like sand and gravel, are highly permeable. Others, like clay, are less permeable.

So, to summarize:

* Aquifers form within permeable layers of soil or rock.

* The type of soil or rock above the aquifer doesn't directly determine its formation.

Let me know if you have any more questions!