Page:Walker (1888) The Severn Tunnel.djvu/134

Rh The fan gave perfect satisfaction during the period of more than four years that it was working; and the same system is adopted for the permanent ventilation of the tunnel; a 40-ft. Guibal Fan having ultimately taken the place of the 18-ft. fan which was used while the works were in progress.

At 5 miles 4 chains the heading was driven east till we reached a distance of only 26 feet from the point where the Great Spring had broken into the heading, coming westwards from Sudbrook.

The heading was almost entirely in the fire-clay shale, and was perfectly dry. The full-sized tunnel was proceeded with and pushed forward over the same length. At the same time the heading was driven westwards from the 5 miles 4 chains pit, and the full-sized tunnel commenced from break-ups at various points, as shown on the section.

At a distance of 800 feet from the shaft the heading passed from the fire-clay into the conglomerate rock, in which the driving was most difficult, both on account of the hardness of the rock and the enormous quantity of water met with. Isolated as this pit was, and short as the lengths of the headings in communication with it were, it required a 70-inch Cornish beam-engine with two 28-inch pumps to keep the workings free from water.

The brickyard which had been established was close to the top of this pit, and the crushing-mill for crushing the shale was connected with the head-gearing of the pit; so that the shale from the