Stirling Sill
Coordinates: 56°07′23″N 3°56′46″W / 56.123°N 3.946°W The Stirling Sill is an outcropping of a large quartz-dolerite intrusion or sill that underlies a large part of central Scotland, and may be contiguous at great depth. The sill is of very late Carboniferous age or more probably Permian, as it penetrates the coal measures, often in bedding planes between the various strata. In places, it rises through fractures in the strata to a new level, forming features that, at the surface, would be called dikes.
At its outcrop on the west, the sill generally lies towards the base of the Carboniferous sequence, and just above the calciferous sandstone deposits and lavas, as can be seen in the upper part of the valley of the Bannock Burn. However, to the consternation of miners, it occupies a higher position amongst the useful strata towards the east, and in places has destroyed the coal, while in others the effect of the sill has been to convert the coal to more valuable anthracite.
The slope of the Abbey Craig, or the Stirling Castle rock, gives a general idea of the angle of dip of the coal measures at the extremity or the coalfield, and the thickness of the sill can also be seen, which is approximately 100 metres.
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