Rowley rag

From the names of Rowley Regis, Rowley Hills + rag.

Rowley rag (uncountable)

1. (geology) A hard basaltic rock found in the Rowley Hills, near Birmingham, formerly used in paving and construction. [from 18th c.]
   • 2004, Robert E Schofield, The Enlightened Joseph Priestley, Pennsylvania State University, published 2004, page 162:

     Rowley-Rag appeared to be the same thing as basalt and toadstone resembled some species of lava.