Played with the file a little bit. It makes some interesting structures but the high level of the Perlin Billows displacement produces broken or ripped texture black areas in the rock. The broken spots resemble cracks but they aren't really "good" cracks because the texture is lost or corrupt in the crack and they look black when direct light is shining into them.
To me this means the displacement needs to be backed off or smoothing turned on in the compute terrain, probably both.