Can't create a hole with the landscape tool.

Hello guys,

So today I started a new landscape, and I wanted to create a hole, then, a cave with meshes, etc… But, when I tried to use the “Visibility” tool to create it, instead of a hole, I got the “landscape hole material” all over the zone, instead of a hole.
I’m sure I’m not really comprehensible, so, here are some screenshots :

So, here is the screenshot.
As you can see, instead of creating a hole, the tool just paint the landscape with the landscape hole material, and, I don’t understand why.

Thx in Advance.