Weir’s Picnic at Hanging Rock is an adaptation of Joan Lindsay’s novel about how the Valentine’s Day picnic of the Appleyard College girls ended badly. Inexplicably, two girls and a teacher disappear—and are never found.
Weir and his screenwriter Cliff Green are good at exaggerating the mystery with atmospheric camera tricks, languorous sensual, and ty, summer heat. The picnic is 4:49 minutes, and the climb to the summit is 10:48 minutes; the rest of the film’s 139 minutes might not exist. We remember these episodes most. When the Appleyard crew arrives at the picnic ground, they s pay no attention to the Fitzhuberts picnicking nearby. Michael Fitzhubert, a man of twenty, eyes the girls but is too shy to approach them. He is the last to see the girls ascending, and he feels guilty about not warning them to be careful. This is incidental to the picnic, though not to the search for the missing girls and other matters, which makes up the bulk of the narrative. 
The summer heat makes the picnickers languorous. Weir exaggerates the girls’ boredom showing them sprawled on the ground like white moths resting on a bare forest floor. He teases that the girls’ attention to one another is mildly sexual. But nothing happens. It’s all suggestive.
Weir couldn’t care less about picnic food. Lindsay’s food is ordinary, snacks on the way of cold lemonade, cold milk, and biscuits, then a lunch of chicken potpie, angel cake, jellies, tepid bananas, iced cake in the shape of a heart, and tea. 
Induced by the primordial ambiance of the rocks, Miranda leads Irma, Marion, and Edith. Edith Fearfully, Edith turns back, but Miranda, Irma, and Marion reach the summit and then disappear. Days later, Marion is found alive but incoherent by Michael Fitzherbert. Miss McCraw, a teacher chaperoning the girls, runs to help look for the girls, but she, too, disappears.
Weir’s choices for music add significantly to the mystery. Gheorghe Zamfir’s haunting Pan-flute powerfully suggests something unknown and deathly is happening.
The cast: Edith Christine Schuler as Edith; Jane Vallis as Marion; Anne-Louise Lambert as Miranda; Karen Robson as Irma; Christine Schuler as Edith Horton.
See Joan Lindsay. Picnic at Hanging Rock. Melbourne: F. W. Cheshire, 1967; Peter Weir. Picnic at Hanging (1975). Screenplay by Cliff Green based on Rachel Lindsay’s novel (1967); Larysa Kondracki. Picnic at Hanging Rock, Episode One, Two, Three, (2018). The screenplay by Beatrix Christian is based on Joan Lindsay’s novel and Peter Weir’s film.
Streaming: https://www.youtube.com/watch?v=Q_qMUNabFaM
*Michael Fitzherbert and his uncle and aunt, Colonel and Mrs. Fitzhubert, are enduring a dull afternoon at Hanging Rock. Their picnic is incidental to the main plot of the girl’s disappearance. There is another traditional garden party picnic at Fitzhubert’s home.