He felt increasingly that his teaching duties were sapping his stamina for focused intellectual labour. There were three standard ways to dig a trench&colon; entrenching, sapping, and tunnelling. Sapping trenches, cannons and gunpowder explosives were a potent force against fortifications. Sapping involved extending the trench by digging away at the end face. A power sapping propeller speed reduction unit is eliminated. This digging was referred to as sapping the enemy fortifications. These characteristics suggest that the younger valleys were formed mainly by groundwater sapping. The town walls were finally breached by a combination of artillery and sapping. The Consu sapping field then saves Roanoke from the Conclave faction's attack. By 1780, serious attention began to be given to the art of sapping and mining. One mechanism that has been advanced is sapping.