Tertiary dyke at Poyllvaaish (dark band of rock
on which hammer rests).
65
million years ago,
at the start of the Tertiary period, the Atlantic Ocean began to form
when North America rifted apart from Europe.
Associated with this tectonic event, the continental plate beneath
northern Britain was heated and cracked open along massive fractures
allowing magma from
beneath the crust to flow upwards. Nowadays, vertical sheets or dykes
of basalt record this event representing where the magma cooled and
solidified within the fractures.
Some of the dykes are over 100 kilometres long and extend more than
25km below the land surface.
