Various theories have been expounded - the most popular being that it is this shape because originally there as meant to be an "opposite" side to it to make a complete tunnel over the tramway, over which the slate waste could have been tipped - but it was never necessary.
This photograph is by grahami and was uploaded December 17th 2009. © grahami please do not copy or distribute without prior express permission.
You can close this window to return to the main site.