Abstract

"The suggestion that the Skye amygdaloidal gabbro represents amygdaloidal basaltic lava in which the grain-size has been coarsened by recrystallization does not imply 'an unusual type of metamorphism' as Bailey supposes. Whereas recent lava-flows are fine-grained, older flows, particularly pre-historic examples, commonly have a doleritic or gabbroic grain-size. Bore-hole investigations in Yellowstone Park indicate that such increase in grain-size is a consequence of the long-continued throughpassage of gases and water escaping to the surface. Bailey's own observation that amygdales within the Skye amygdaloidal gabbro 'interrupt the form of the bigger feldspars' provides evidence that the bigger feldspars are younger than the amygdales, and that the rocks containing them have therefore recrystallized."

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