Wasn't it originally built to be gravity balanced (dual track) but due to a minor miscalculation of angle of slope towards the lower end (causing wagons "stalling" ) eventually converted to single track (powered).
Having a variety of power sources over the course of the quarries life ...from steam power (the remains of which can still be seen in the entrance to the incline) to diesel wagon lorry power ...
ending up with the electric motor from the dressing sheds being moved twixt incline and shed power duties towards the quarries final days ???