Ymenyn Y Tylwyth Teg Or Fairy Butter

: Welsh Folk-lore

I cannot do better than quote Pennant on this matter. His words are:--

Petroleum, rock oil, or what the Welsh call it, Ymenin tylwyth

teg, or Fairies' butter, has been found in the lime stone strata in

our mineral country. It is a greasy substance, of an agreeable

smell, and, I suppose, ascribed to the benign part of those imaginary

beings. It is esteemed serviceable in rheumatic cases, rubbed on the

parts affected. It retains a place in our dispensary.

Pennant's Whiteford, p. 131.