What is "whinstones"

Usage examples of "whinstones".

The stars burned with a lidless fixity and they drew nearer in the night until toward dawn he was stum­bling among the whinstones of the uttermost ridge to heaven, a barren range of rock so enfolded in that gaudy house that stars lay awash at his feet and migratory spalls of burning mat­ter crossed constantly about him on their chartless reckonings.