Nature
Nature is a central theme of Picnic at Hanging Rock. The characters come into direct, violent contact with the power and mystery of nature. Lindsay reinforces this idea by drawing attention to numerous details in the natural world surrounding the girls, including beetles crawling on Miranda's leg and a lizard curled on Marion's arm. In addition, she makes repeated references to the smallness of the human characters in comparison to the overwhelming scale of the natural world, which vastly predates them, particularly the strange physical formation of Hanging Rock itself. Lindsay uses these observations about nature to remind the reader of how small the events of the story are in comparison to the vast scale of geological time and natural phenomena. This adds to the story's central mystery as it highlights nature's capacity to elude human understanding.
Gossip
Gossip is also a significant theme in the book. Following the disappearance of the girls and their teacher, various news publications write sensationalizing headlines about the story, saying that they were kidnapped or murdered. This attracts a great deal of attention and eventually results in the story getting international coverage. This greatly unnerves Mrs. Appleyard, who knows this bad publicity will have negative consequences for the school. The book demonstrates the way in which gossip spreads from local rumor to news headlines, focusing specifically on how the spark of scandal can quickly turn into a wildfire of speculation.
The Supernatural
The supernatural is also a primary theme in the novel. The central mystery of the story is never solved. The girls and their math teacher vanish without leaving behind a trace of physical evidence. No one actually present during the afternoon of disappearances can clarify, or even fully recall, what happened. The brief glimpses that the narrator offers of the events leading up to the vanishings are equally cryptic: three of the girls travel towards the monolith seemingly in a trance; Miss McCraw is said to have run up the rocks in her underwear. In not revealing the cause of the disappearances, Lindsay creates an atmosphere of unease while also suggesting that the events at Hanging Rock are beyond normal human comprehension. The unresolved ending underscores the power of what can't always be explained.
School Social Dynamics
School social dynamics are another important theme in the book. The girls enrolled in the school all occupy specific roles in the community. Miranda is well-loved and popular, often looked to as a leader and a source of stability. Marion is academically strong and viewed as the brightest pupil with a relentless desire for knowledge. Irma is a beautiful heiress to a family fortune; she is expected to marry well and live a life of luxury. They are all admired for these various qualities. In contrast, their friend Edith is described as both plain-looking and not very smart; no one relies on her or particularly enjoys her company. Lindsay depicts the way in which the girls create a social hierarchy within the school and use it as a means of categorizing who has value and, rather unkindly, who does not.
Queer Desire
Another theme in the book is queer relationships. The novel spends limited time on overt romantic relationships. The story begins on Valentine's Day and two of the domestic staff get married and leave the school. However, there are various intense relationships between the girls at school. In particular, Sara Waybourne holds a strong affection for Miranda that appears to be romantic. She has a picture of her in her room and is thrown into a deep depression after her disappearance. Later in the novel, she is driven to such despair that she runs off for several days and is subsequently found dead, apparently of suicide. Lindsay explores the way in which this unrequited queer relationship not only cropped up but was actually fostered by the closeness of the girls' school environment.
Propriety
Propriety is a major theme in the novel. Mrs. Appleyard is not particularly troubled about the well-being of her students; instead she is mostly worried that their disappearance will impact her and the school's status. She shows a similar outlook before the incident, fixating on minor rules and doling out harsh punishments for small infractions. She clashes with teachers who do not agree with her on academic and disciplinary measures. Her characters show the way in which the upkeep of good manners can be entirely divorced from being a good or compassionate headmistress.
Wealth
Wealth is another key theme in the book. Mrs. Appleyard is afraid of losing Irma as a student because her father is rich and his donations significantly assist the school in staying afloat. As a result, Mrs. Appleyard extends numerous courtesies to Irma that she does not to other students, including being more lenient about the rules and frequently bragging about her attendance at the college. In contrast, she treats less wealthy students, like Sara, more harshly, not hesitating to immediately withdraw them from classes and activities if their parents are behind on tuition payments. The book captures the unappealing ways that money plays a huge role in how students are treated at Appleyard.
