1. plural of shale; fine-grained sedimentary rocks that split easily into thin layers
Usage: geology

Examples

• The geologist examined several different shales from the quarry.
• Oil companies often drill through shales to reach petroleum deposits.
• These shales contain fossils from millions of years ago.
• The hillside was composed of dark gray shales that crumbled easily.
• Shales are common sedimentary rocks found in many regions.
• The construction crew had difficulty building on the unstable shales.