It has been proposed that the Watchung basalt flows of the Watchung Mountains are extrusive eruptions of the same magma that created the Palisades Sill.
42.
The presence of alteration in all of the extrusive levels but the very highest imply a succession of numerous hydrothermal convection cells active during eruption.
43.
At Tievebulliagh, Northern Ireland, porcellanite is a tough contact metamorphosed hornfels formed from a lateritic soil horizon within a basaltic intrusive / extrusive sequence.
44.
It grows on sandstone, intrusive and extrusive igneous rock such as granitics, in all kinds of exposures to sunlight, including vertical rock walls.
45.
Volcanic bombs are extrusive igneous rocks ranging from the size of books to small cars, that are explosively ejected from stratovolcanoes during their climactic eruptive phases.
46.
Intrusions are one of the two ways igneous rock can form; the other is extrusive rock, that is, a volcanic eruption or similar event.
47.
Mineralization occurs either as structurally controlled veins and breccias discordant to the stratigraphy and less commonly as stratabound mineralization either in extrusive rocks or permeable sedimentary facies.
48.
Very smooth plains material flanks some scarps and ridges and, if the material is ponded extrusives or mass-wasted products, may postdate the structures.
49.
Generally, the mineral constituents of fine-grained extrusive igneous rocks can only be determined by examination of thin sections of the rock under a field.
50.
The primary igneous rock on the Wrekin is rhyolite; this has a pinkish colour and is usually banded as it is a slow cooling viscous extrusive rock.
