Entrance to former canal spur to former Black Park Collieries Railway, later the Glyn Valley Tramway Dock. Now sealed with brickwork where the canal arm left the main canal channel under the towing-path. The area of the rectangular canal dock at right-angles on the east side of the canal occupied the southern part of what is a large water basin at the Chirk sewage works (just north of the wood-chip plant).

The original 1870s horse-worked railway from the slate quarries at Glyn Ceiriog ran along the valley bottom of Glyn Ceiriog and under the Chirk Aqueduct to a canal wharf further to the south east at Glendrid. In the 1880s steam locomotives were introduced and the eastern end of the line re-aligned so that it ascended to Chirk Village and connected with the main standard-gauge locomotive railway near Chirk Station and the redundant Black Park Collieries Dock Basin on the canal. The Black Park Collieries Railway was an early nineteenth-century horse-worked railway that ran eastwards from the dock for over a mile to collieries north-east of Chirk.

INW 4-2007 & Stephen R. Hughes, 25.05.2007.