Crack/Break in Custom Worldspace

[kremlinjoe]

I'm trying to create a custom worldspace but I seem to have encountered a problem. I used a height map to generate the landscape and I've noticed that all around the edges of the generated landscape there is a sharp drop in height and this appears to have caused a crack or break in the landscape.

 

http://i.imgur.com/uQjNB.jpg

 

http://i.imgur.com/fLvW0.png

 

Unfortunately I've only just noticed this problem and have pretty much finished cluttering the landscape etc. so i'm wondering if this can be fixed without starting over.

 

Any help is much appreciated.