This is a set of 8 fake stone shaders racked up to give complete coverage of a surface that you can control via a surface layer or distribution shader. The fake stones range in shape and scale from .01 meters - 1 meter, respectfully.
I've had the common problem of small, lower stones displacing the surfaces of larger stones above them for a while. This method eliminates that problem.
It is based on FrankB's suggestion of using a merge shader's 'choose by altitude - Highest (raise)' method
http://forums.planetside.co.uk/index.php?topic=3796.msg41840#msg41840 to merge 2 fake stone layers together without the bleed-through from below. A fantastic tip, thanks!
I've used this idea to the power of 7 merge shaders, combined into one surface.
For the correct way to wire this to your scene, just add a new surface layer to the end of your shaders list, uncheck apply colour and stick 'Final Merge Shader' into it's child socket(example image attatched). Now just use the surface layers distribution parameters for control.
Hope you have fun with them!
P.S: The textures here are designed for an algae-covered riverbed(as that's my latest old haunt I'm revisiting
), just change the 4 'stones texture' colours/displacements to suit. The scales are all good, I think, so they probably don't need much tinkering there.
The larger stones might need a little more displacement as I can see some sharp edges/corners...
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