But most of the surface is covered by a thin sheet of boulder clay.
The valley bottoms have a thin deposit of boulder clay.
The superficial deposits are of boulder clay, which provides material for making bricks.
A material called boulder clay is deposited on the floor of the valley.
When the ice finally retreated it left deep deposits of boulder clay (or till) behind.
The surface was some sort of boulder clay.
Glacial till is still widely known in Britain by the older name of boulder clay.
The valley was subsequently filled with boulder clay and gravel.
It is situated on a plateau of boulder clay left by the glaciers about 300,000 years ago.
He again attracted attention by adding fossils from the local boulder clay to his earlier collection.
But most of the surface is covered by a thin sheet of boulder clay.
The valley bottoms have a thin deposit of boulder clay.
The superficial deposits are of boulder clay, which provides material for making bricks.
A material called boulder clay is deposited on the floor of the valley.
When the ice finally retreated it left deep deposits of boulder clay (or till) behind.
The surface was some sort of boulder clay.
Glacial till is still widely known in Britain by the older name of boulder clay.
The valley was subsequently filled with boulder clay and gravel.
It is situated on a plateau of boulder clay left by the glaciers about 300,000 years ago.
He again attracted attention by adding fossils from the local boulder clay to his earlier collection.