© Andrew C. ParnellBen Bulben, County Sligo, Ireland.
Mount Augustus in Australia is an example of a sandstone monolith that could be the largest of those monoliths that also includes Uluru. Mount Augustus, or
Burringurrah to the local Wadjari people, is an asymmetric anticline resting on top of what geologists refer to as "very old" granite. Its composition differs markedly from the underlying rock strata.
Ben Bulben is an example of another isolated monolith, or tor, that can be found on every continent. They all share similar morphology, although they are composed of different minerals. Mount Augustus, for instance, is made up of rocks and pebbles of various sizes cemented together by hard sandstone. In other areas of Australia, such as
Bald Rock, the great blocks of stone are actually granitic, resting on top of discontinuous strata that does not match the overall structure of the rock.
The geology of
Ben Bulben is quite different, however. It is composed of Darty limestone (which makes up the Darty mountains) and shale, overlying Glencar limestone. Ben Bulben is the headland of the Darty mountains, sloping gradually upward until the
flat-topped mesa and steep, regularly carved cliff face stop at the edge of the ocean. The change from Ben Bulben shale to
Glencar limestone in the monolith is dramatic - the boundary layer is paper-thin.
In other areas of the world, such as
Peña de Bernal in Mexico, or the
Rock of Gibraltar in Europe, the single stones appear to be metamorphic, indicating a powerful energy source that drew the material in the mountains together, as well as melting and reforming their mineralogical composition. The Rock of Gibraltar is composed of metamorphosed limestone and chalk. The Strait of Gibraltar, itself, demonstrates some
remarkable topography and could mark an area where Earth-grazing electric arcs touched-down and
sculpted the region.
Comment: Tune in to SOTT Talk Radio this Sunday 15th December when we'll be discussing all this and more with Wallace Thornhill from the Thunderbolts Project.