unsatisfactory mountains

[Revock]

Irregardless of the colors or textures i chose, I'd like advice on a problem with mountains i'm encountering.

I can't seem to generate them without a smooth border surrounding them, i suppose i must be feathering the heightfield selection too much. The map i'm working on is intended to be a series of overlays in Auto Realm which i used to generate the landmasses and ocean, here's an Auto Realm shot of the overlay added.

I originally wanted to work with Wilbur heighfields colored using Torq's "Mountain Techniques using Wilbur and Gimp" but the problem i had there was conforming it to my AR map contours.

*edit* most of the heightfield generation was done using RobA's "simple mountains using Gimp" Tut, the darker brown mountain was generated by Wilbur, embossed with the RobA instructions.