Related Clues:

• Rock source of petroleum
• Coarse-grained rock that splits easily
• Thin-layered sedimentary rock
• Hospital in transaction for source of gas
• Rock involved in fracking
• Rock is first thing for teenagers after school
• A strong leader and hearty too, perhaps, with many layers.
• Rock a prince found in the Kent area
• Rock formed from compressed mud
• Quiet beer possibly source of gas
• Namely this, metamorphic?
• Soft rock prince found in the Kent area
• Fossil rock