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.