In the western portion of Mainland, in Northmavine, -there is a considerable tract of rocks of this age which are formed largely of intrusive diabase-porphyrite; similar volcanic rocks occur in Papa Stour.
The Old Man presents a characteristic section, for it exhibits a thick pile of massive, current-bedded red sandstones, resting, near the foot of the pinnacle, upon a thin bed of amygdaloidal porphyrite, which in its turn lies unconformably upon steeply inclined flagstones.
Quartz Porphyry Pp. Porphyrite d Gr.
In China, at the close of the period, there were enormous eruptions of melaphyre, porphyrite and quartz-porphyry.
They comprise Seil, Easdale, Torsay, Luing and Shuna, and owe their name to the fact that they are composed mainly of metamorphic rocks, Easdale, Torsay and Luing being entirely slate, Seil mostly slate with some porphyrite in the north, and Shuna gneissose.
- The ancient or plutonic igneous rocks (including granite, syenite, diorite, gabbro, porphyry, porphyrite, norite retinite) appear at various points of the two previously described regions.