Summary:
Deepslate transition starts too high which does not match old chunks. It must start at Y = 4, not Y = 8. Only then will the transition match the bedrock.
Steps to reproduce:
Create a world in 1.17.
Upgrade to the latest pre-release.
Compare the deepslate transition in new chunks and old chunks.
Observed results:
The deepslate transition in new chunks starts too high compared to the old chunks.
Expected results:
The deepslate transition will be the same in both old chunks and new ones.
Image:
[media][media]
Probably intended to make a better transition between 1.17 deepslate blobs/patches and 1.18 deepslate transition.
It also allows deepslate coal ore to generate so it's fine.