Having difficulties with voxel Terrain/Biomes

Hello, I've been looking into various voxel setups, and have begun looking into a couple of tutorials

specifically this one (http://forum.unity3d.com/threads/tutorial-procedural-meshes-and-voxel-terrain-c.198651/)

the code provided/created is proficient at creating a terrain of 2 types of blocks (grass/stone) But its very choppy and generally uniform.

How would/could I go about making certain areas smoother/possess distinctive qualities (IE flatlands/mountains)

Alternatively any information as to where I would research how to do this would also be appreciated

thanks in advance