Salt of the Earth

The Third Doctor and Jo Grant arrive for a well-deserved holiday of sun and "blokarting" on a salt lake in Australia in 2028. Weird sculptures adorn the landscape — statues carved from the salt. People have been leaving them in the salt lakes for years — but these look different. Grotesque, distorted figures twisted in pain. They don't last long in the rain and the wind, but they're just made of salt... Aren't they?