The end of limestone deposition in the Isle of Man was marked by the explosive eruption of a volcano which formed the basaltic rocks now exposed between Scarlett and Poyllvaaish.
Vents and fissures along which magma flowed to surface can be seen in the area around Scarlett Point.

Basalt lava and ash are erupted from a volcano which form the Scarlett volcanics at Castletown	Lava erupted under water can form pillow-shaped structures, rather like toothpaste being squeezed out of a tube
Dykes are fissures in which magma solidifies before reaching the surface

This photograph shows volcanic rocks at Poyllvaaish