The vegetated ravine and plunging waterfall in France were captured by John Ruskin as he contemplated the secret sexual fears that helped destroy his marriage.
The “erotic” drawing’s position at the heart of a girls’ school in York was also kept secret.
Ruskin drew La Cascade de la Folie in Chamonix in 1854 after escaping England where his wife Effie had applied to end their unconsummated six-year marriage.
The drawing, an expert said, was one of the most obvious examples of the artist translating landscape formations into the “normally concealed parts of a woman’s body”.
