This geological feature would focus on the borrow pits excavated during the Ponds Project to source the 30,000m³ of London clay needed for dam raising. The article would explain what borrow pits are – excavations left after material has been dug for building embankments – and how their use represented an innovative approach to sustainable construction. The piece would trace the fate of these pits, how they were landscaped and planted, and explore the geological significance of London clay. It would also touch on archaeological discoveries during excavation, including a famous Mark 3 Ford Cortina found on the bottom of one pond.