A ‘terril’ is a heap of stone, popularly called “het stort” (‘the dump’). Terrils contain stone detritus that has been washed out of the mined coal and has been dumped into a heap. Over time, the terrils became so high that they’ve become landmarks in the landscape of the former mining region. These mountains of stone still contain some coal, so the Winterslag terril has been washed again at the end of the 1990s and in the early 2000s.

Terrils are ideal places for scouting for fossils from the Carboniferous period.

These heaps of gravel also are an ideal biotope for moss and lichen. A terril is sometimes called a living laboratory. The industrial waste is an ideal breeding ground for lime-loving lichens and for other unique, pioneering vegetation.