The arch at the southern end of Langness was formed relatively
recently by the erosive power of the sea. However, of greater significance
to geologists is the presence of an ancient land surface known as
an unconformity.
The lower half of the arch is made up of Manx
Group rocks formed around 480
million years ago while the upper half is a type of gravel deposited
by flash floods in the Carboniferous period, around 350
million years ago. The uneven surface separating these two rock
types is the unconformity and represents a gap in time of around
135 million years when no rocks have been preserved. The area was
sub-sequently submerged below the sea leading to deposition of the
Castletown Limestones
on top of the gravel.
