West Derby acre

In Lancashire, England, a unit of land area = 9000 square yards. It is based on a perch of 56¼ feet.

John Chalmers Morton.
A cyclopedia of agriculture, practical and scientific: in which the theory, the art, and the business of farming are thoroughly and practically treated. Vol. 2.
Glasgow: Blackie and Son, 1855.
Page 938.