The legendary origin of slate as a roofing material centers on Saint Lezin, the French Bishop of Angers. Caught in a sudden storm, on a pilgrimage to Rome, he is said to have improvised protection by arranging, tent-like, slabs of outcropping rock along the pathway. In a later vision, he was instructed in the use of these rocks for the roofing of houses (head-lap etc.).
For the Bishop to achieve sainthood a “miracle” was required. This occurred in the 9th century when the Thatched Roof trade (the equivalent to modern 3-tab shinglers) were resisting the upstart slate industry. As he rode through the Angers slate region he saw a huge mass of rock shearing off a quarry wall. He held his staff aloft and at his command the rock was suspended in mid-air, while the workers below fled to safety.
Convinced by this divine manifestation, the nay-sayers were silenced and the slate industry flourished thereafter.
This story was recounted in a 1928 publication, The Peach Bottom Slate Quarries Project, Harford County, MD. There is no way to verify the account, but the bottom line is…we got a Saint! Who’d–a-thunk? — Jozef Djzula, Ruff Roofing