Here is a quote from Mary Webb's novel Armour Wherein He Trusted:
"I come from Cymru, sir, and my home is in the waste; and my lineage is elf-lineage, and for our sign, it is a churn-owl with a kingly crown upon his head."
"Where, then, is this waste situate," asked the ascheater...
"Sir," she made answer, "it lies between Salop and Radnor. It lies also between life and death. It is betwixt and between all things."
"Is it in Doom Book?"
"Nay my lord, for it is in neither county. Nor is it in any hundred, nor does it pay gold."
"How comes that?"
"Why, lord, it is faery ground and you cannot measure it nor go round it, for though it is only a narrow piece, times, of the width of three horses head and tail, yet, times, it will widen to eternity and yet again it will shrink to a knife-edge."