This trip was originally done by gravity! The route, with the final mile across the man-made embankment known as The Cob, relied on gravity to enable the loaded slate trains to get to port. Horses were used to haul the empty wagons back to the mine. On the return trip, they rested and fed in the 'dandy' wagons. 'The 23 1/2" (597mm) gauge, corresponding to that being used in the quarries, was wide enough to allow the horses to work efficiently when pulling the empty wagons and narrow enough to enable the Railway to negotiate the sharp curves made necessary by the mountainous terrain. The wagons were small enough to be loaded easily and man-handled in the quarry and at the port.' (From the traveller's guide.)