Slope Shaft
A slope shaft is a quarry entrance, dug in to the ground at an incline. Often they include pedestrian access via steps as well as rails for a cart used to extract the quarry's product.
More information
Brewers Yard Quarry - Brewers Yard Quarry has a very narrow slope shaft
Slope Shaft Photo - A photograph looking down a slope shaft
Box Quarry Fact Sheet - More details about underground quarrying