The system known as 'longwall' gradually replaced pillar and stoop during the 19th century in the east of scotland, but had been in use in Lanarkshire and West Lothian since the 1770s. There are many different methods of longwall mining, however, the most obvious difference is that in longwall, all the coal is removed leaving nothing to support the roof.
As the work progresses and the unsupported area behind collapses under the weight of the overlying rock above. The one place that had to be kept supported were the roadways leading to the coalface to allow transport of the coal in waggons to the mine shaft. Fallen rock was built up to form supporting walls; rock from the roof was also stripped from the roof as it collapsed to maintain the height of the roadway.
The diagram below shows two different systems. At the top, the coalface is advancing away from the mineshaft (the lighter area shows where the coal has been extracted). At the bottom, is a system more often used near the boundary of a coalfield where the coal is removed from the furthest part, working back towards the mineshaft.
A big disadvantage of longwall was the damage done at the surface by subsidence. It has a serious effect on buildings and fracturing of the rock could allow water in to the coalworkings.