These slag heap formed a chain about a quarter of a mile long on the south bank of the river, opposite the Malleable. The white colour suggests they were of blast furnace slag from Thornaby Iron Works, but it is also possible that they came from the blast furnaces belonging to Bolkow Vaugn at Newport. They were situated just off the rail track from Thornaby to Middlesbrough so the suggestion is quite feasible.
What puzzles me is how these heaps came to be so high. Slag is normally transported in molten form in small cast iron trucks called slag ladles, in which the temperature is about 1000 deg C . It is then tipped out, flowing like molten lava. I cannot see how a steam locomotive would be able to get to the top. Was there some kind of moveable cableway, as was used in Blacketts brickyard?
Photograph and details courtesy of Fred Starr.