to descend. The descending loaded wagons then returned the ballast wagons to the top of the incline. One of the major inclines at Dinorwic had four parallel tracks, two worked by the ballast method and two as conventional gravity balance. Types Inclines are classified by the power source used to wind the cable. Stationary engine A stationary engine drives the winding drum that hauls the wagons to the top of the inclined plane and may provide braking for descending loads. Only a single track and cable is required for this type. The stationary engine may be a steam or internal combustion engine, or may be a water wheel. Gravity balance In a gravity balance system two parallel tracks are employed with ascending trains on one and descending trains on the adjacent track. A single cable is attached to both trains, wound round a winding drum at the top of the incline to provide braking. The weight of the loaded descending cars is used to lift the ascending empties. This form of cable railway can only be used to move loads downhill and requires a wider space than a stationary engine -driven incline, but has the advantage of not requiring external power, and therefore costs less to operate. Trwnc inclines A variation of the gravity balance incline was the trwnc incline found at slate quarries in north Wales, notably the Dinorwic Quarry and several in Blaenau Ffestiniog. These were worked by gravity, but instead of the wagons running on their own wheels, permanently attached angled wagons were used that had a horizontal platform on which the slate wagons rode. Water balance This is a variant of the gravity balance incline that can be used to move loads uphill. A water tank is attached to the descending train. The tank is filled with water until the combined weight of the filled tank and train is greater than the weight of the loaded train that will be hauled uphill. The water is either carried in an additional water wagon attached to the descending train, or is carried underneath a trwnc car on which the empty train sits. This type of incline is especially associated with the Aberllefenni Slate Quarry that supplied the Corris Railway. This form of incline has the advantages of a gravity balance system with the added ability to haul loads uphill. It is only practical where a large supply of