By the Early Devonian the Iapetus Ocean had closed and was replaced in northern Britain by an essentially transtensional regime with sinistral shearing, and accompanied by major igneous activity.
However, enormous emphasis has been placed on them for understanding igneous processes and the evolution of Earth.
The occurrence of these felsic extrusive igneous rocks potentially provides key information on the complex interplay of magmatism and tectonics.
This heat gradually accumulates and eventually causes localized eruptions of basaltic magmas (molten igneous rock).
It is an igneous or fiery aura, not indeed in the open act of combustion, but composed of the finest and most minute particles of a peculiar species of elementary fire.
The layering in these ultramafic rocks, and their position above mantle tectonites, is attributed to lower crustal igneous processes.
Below the lowest sheet of largely coherent mafic igneous rocks is the Phyllite-Quartzite Group, a sequence of turbidites and black mudrocks.
Major crustal rifting has also played a part in the evolution of large bodies of Proterozoic sedimentary and igneous rocks.
On Macquarie Island there's very similar kind of geology, as I'm sure Rick has described; we have mantle rocks and evidence of punctuated deformation events in igneous activity.
The prevalence of Late Jurassic subduction-related igneous rocks indicates that arc formation and accretion orogeny were the most important processes during the evolution of this part of the Internal Hellenides.