I do not know whether this has been observed before, A compleat and faithful edition of the works of this great father of English poetry, with an accurate verbal index, as well as glossary, is much to be desired.
137. Miraculous combustion of wood without ashes, and oil without smoke.
There was in Kildare an ancient monument named the fire-house, wherein Cambrensis saith, was there continual fire kept day and night, and yet the ashes never increased. I travelled, says Stanihurst, of set purpose, to the town of Kildare to see this place, where I did see a monument like a vault, which to this day they call the fire house. (Holinshed's Chronicles, vol. 6, p. 38. Edit. 1808.)
The secret of this miracle had been lost at Kildare, but had Stanihurst (to use one of his own words) pilgrimaged to the monastery of N. Señora de Valvanera,