Related Clues:
- Product of clay compaction
- Saber-toothed cat catcher
- Introduction of secure, healthy, source of gas
- Oil source has damaged the French
- Some mudrock
- Frackable rock
- Rock formed from clay
- Earth's crust, mostly
- Rock in which fossils can be found
- Rock source of petroleum
- Thin-layered sedimentary rock
- Hospital in transaction for source of gas
- Rock involved in fracking
- A strong leader and hearty too, perhaps, with many layers.
- Certain fossil preserve