Yep, the symmetrical lattice (I tend to get absent-minded 'bout those nasty technical terms grin) As to the fractal thing, you can probably use one of the fractal setting in the Terrain Editor, and the cliping bracket is found on the right-hand side of the big editing window where you do painting effects on the terrain's grey-scale image. By moving the upper and lower ends of the bracket, you 'clip' off either the highest or lowest points of your terrain, and with a good fractal, that would crate the holes in the clouds you're looking for.

RosemaryR
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"This...this is magnificent!"
"Oh, yeah. Ooooo. Aaaaah. That's how it starts.
Then, later, there's ...running. And....screaming."