Easiest Way to Detect Slope of Environment

Hi, I have a character that is just a simple sphere that rolls and jumps around the level. Whenever he jumps, he can control himself in midair.

I have a part of my player movement script that detects when the player is colliding with an object to allow it to jump, and not allow it to jump when not colliding

function OnCollisionStay(col : Collision)
	letJump = true;

function OnCollisionExit(col : Collision)
	letJump = false;

The problem with this is that when the player falls off the level and collides with anything on the way down(such as a cliffside), it allws him to jump, thus giving him a way to jump back up the wall, which is what im trying to aviod.

What would be the easist way to prevent this? I attempted to try a DrawLine without much success.

Any insight or information that could point me in the right direction would be greatly appreciated.

Thanks again!

EDIT: Let me know if you need any further info to help you!

You could set a Tag on all objects that allow the player to jump and in your Collision var check this tag and see if it is a jumpable object.