The opening scenes of the novel take place by the Shivering Sands, which are a huge area of quicksand on the coast of Yorkshire, just a short walk from the Verinders' country house. It also becomes both the hiding place for the most important clue leading to the discovery of the truth, and the place where Rosanna commits suicide. This is Betteredge's first description of it:
The tide was on the turn, and the horrid sand began to shiver. The broad brown face of it heaved slowly, and then dimpled and quivered all over. (22.214.171.124)
Betteredge hates the Shivering Sands – it kind of creeps him out, as you can tell from the description. He also personifies the Sands when he talks about its "broad brown face." It's as though the Sands are alive. Rosanna thinks so, too. She says that,
"It looks as if it had hundreds of suffocating people under it—all struggling to get to the surface, and all sinking lower and lower in the dreadful deeps!" (126.96.36.199)
To Rosanna, the Sands seem alive because they're hiding hundreds of suffering faces. To Betteredge, the Sands themselves seem to be one single, "broad brown face." What do the two images each suggest to you?
The Shivering Sands are also dynamic (constantly changing), and that's part of what makes them so scary and creepy. But Rosanna finds the dynamism exciting:
"Isn't it wonderful? isn't it terrible? I have seen it dozens of times, and it's always as new to me as if I had never seen it before!" (188.8.131.52)
Rosanna likes the fact that the Shivering Sands are always different: they always look "new" to her. But it's both "wonderful" and "terrible" at the same time.