Some info about the Little Hulton Slags:
"It was the biggest stuff rook in the world and the tip for colliery waste from several pits belonging to Manchester Collieries Ltd that were situated in Tyldesley, Walkden and Little Hulton, including what was the biggest colliery in the now defunct Lancashire coalfield: Mosely Common."
Some more information, Someones personal account:
"The colliery waste tips of the former UK coalfields were often smouldering: spontaneous combustion of small coal within the tips shale was the cause. The stuffrooks at the back of my grandma's were one of my playgrounds as well. They too were always on fire.
They were constantly sprayed from rusty old pipes with water that was pumped up from the pit that had created these rooks but which had closed in the 1930s. The pit served as a pumping pit for other local collieries that were still functioning when I was a child. The water from the pits was usually a bright orangey-yellow colour caused by the iron pyrites in the bands of ironstone that is often found within Lancashire coal seams. We called such water "okreh water", a Lancashire corruption of "ochre water" no doubt. A good example of "okreh water" can still be seen at Worsley where the Bridgwater Canal water is coloured fby the pit water draining out of the coal workings at Worsley Delph.
The sulphurous smell of the old tips, mentioned above by pOb36, was because most Lancashire coal did in fact have a high sulphur content. Sometimes the fires within the tips had burned so fiercely over the years that only a thin surface crust of shale was left and it happened not infrequently that people - all too sadly often children - fell through this crust to their deaths. That's why watchmen used to chase us off the smouldering rooks of my childhood. However, the coal companies, and later the National Coal Board, made use of this spontaneous combustion because the bright red shale left after the rook had burnt out was sold as an aggregate that was very useful for road building and making tennis courts. The "Old Man of Parr", a bright red shale outcrop of a burnt out rook was the only remnant of the once extensive Ashton's Green Colliery (closed in the early 1930s)in Parr, St. Helens when the Derbyshire Hill council estate was built around it. It has been long since landscaped. Likewise the "Seven Sisters" at Bryn, which I knew as the "Wigan Alps": they were formerly huge mountains of waste from the Garswood Hall Colliery (closed 1953)."