Amethyst Terrain Generation

Put the summary of the bug you're having here

What I expected to happen was...:
With the new Amethyst underground areas, they should be spawning underground

What actually happened was...:
The Amethyst area spawned above the ground inside a river. I haven't been able to find another one so far so I'm not sure if this is a one-off thing

Steps to Reproduce:
1. Make a new world, default settings using this seed: -2647750233945315423
2.  Travel to 56 67 -149
3. ...