This brick tube would continue into the mountain for another 883 feet. It was at that point that the more stable rock would support a brick arch. The total distance into the mountain for the brick tube and arch is 7573 feet.
It is needless to say that this type of construction required a lot of bricks. Some twenty million bricks were made and used in the construction on the west end. There was a brickworks built to supply the construction just to the south of the west portal area.
The following three photos show the brick tube at west portal and the brickworks buildings at the height of their production.