Picnic at Hanging Rock by Joan Lindsay

It was a cloudless summer day in the year 1900. Everyone at Appleyard College for Young Ladies agreed it was just right for a picnic at Hanging Rock. After lunch, a group of three girls climbed into the blaze of the afternoon sun, pressing on through the scrub into the shadows of the secluded volcanic outcropping. Farther, higher, until at last they disappeared.
Mysterious and subtly erotic, Picnic at Hanging Rock inspired the iconic 1975 film of the same name by Peter Weir.

Penguin Books 1978 paperback in great condition.