Brindley's technique minimised the amount of earth moving by developing the principle of contouring. He preferred to use a circuitous route that avoided embankments, and tunnels rather than cuttings. Though this recognised the primitive methods of earth-moving available at the time, it meant that his canals were often much longer than a more adventurous approach would have produced. But his greatest contribution was the technique of puddling clay to produce a watertight clay-based material, and its use in lining canals. Puddle clay was used extensively in UK canal construction in the period starting shortly after his death. Starting about 1840 puddle clay was used more widely as the water-retaining element (or core) within earthfill dams, particularly in the Pennines.