Direct3D - 9: Shading Issue

[Framework]

I've created a terrain-loading application that loads a 3D-terrain file. The mesh displays perfectly fine, but the shading I've selected (gouraud) isn't functioning properly. Here's a screen-shot:

http://s18.postimage.org/gw952z4ex/Shade.png

As you can see, it looks pixelated, which isn't what I want. Any ideas as to why the shading effect isn't working?

Thanks :)

_Wazzak