Related Clues:

• Tools for establishing flat surfaces
• Devices to establish flat surfaces
• Layers or thicknesses of earth
• Layers of rock in earth's crust
• Layers as of rock in the earth's crust
• Thicknesses of material - or hens?
• Thicknesses - or hens
• Layers of rock on earth's surface
• Layers or social classes
• These hens produce eggs
• Devices to check if surfaces are flat
• Columns
• That's what happens if you give a firm turn to the poor brutes
• Fifty elves have no inclination to be like them
• Lines, by the sound of them