The crust is the outer hard layer of the Earth.

The work of digging halted due to a very hard layer under the earth.

When the troops came in afterwards, they found a hard layer of muddy glass on the ground where the buildings had melted.

A very hard layer of rock can form a temporary base level, until it is cut through.

That hard layer of stone eroded more slowly than the underlying materials.

All together, these pieces make a hard layer around the insect's body.

Below four to six inches, he said, lies a hard layer called laterite.

Helmets are made in two main layers: hard and energy-absorbing.

This may cause tiny tears or cracks in the hard outer layer of the disc.

Duricrust is a hard layer on or near the surface of soil.