The characteristics of this stone led to the development of small open cars that carried the slate in its various forms.
These were first developed on the narrow gauge railways serving the slate industry of North Wales in the late 18th century.
They were initially used on horse-drawn tramways, but survived with only minor modifications into the days of locomotives and are still to be found in use in the 21st century.
Early designs used simple wooden rails to hold the packed slates.
They typically consisted of a basic flat wagon with a three-sided iron body that held the waste.