James O'Leary, The Most Ancient Lives of Saint Patrick… (1874)
“ From that day forth are these stones found useful unto no building; but if should any one thereunto dispose them, suddenly would the whole work fall down and tumble into pieces. And they admit not the heat of any fire, nor, when plunged into water, do they hiss like other stones; whence it hath become a proverb in that country, when at any time a stone falleth from a building, that it is one of the stones of Usneach. ”
