Symbolism is where a description or reference stands for something more than the physical object itself. The Standing Stones are used symbolically throughout the novel.
They are first described in the Prelude as dating from the time of the Druids, before the coming of Christianity. The implication is that they are associated with some kind of lost, ancient wisdom.
The theme of how human life constantly changes is emphasised throughout the book. In contrast, the Standing Stones are unchanging –
The Standing Stones pointed long shadow-shapes into the east, maybe just as they'd done of an evening two thousand years before.
At the start of Seed-Time, reflecting on how her father's death has changed her life, we are told that
this old stone circle, more and more as the years went on at Kinraddie was the only place where ever she could come and stand back a little from the clamour of the days.
Often she makes physical contact with the Stones as if with a loved one –
she went and leant her cheek against the meikle one. Sometimes the Stones are personified.
After her row with Ewan at the end of Seed-Time, for example,
she ran and panted, the Standing Stones wheeling up from the whins to peer with quiet faces then in her face.
Paradoxically, the stones represent permanence (in their solidity and stature) but also transience – they represent a marker for modern civilisation and the lost ways of the ancient hunter-gatherer nomads. They are used to make a permanent memorial for what has been lost at the end of the novel.