What is the origin of the vesicular structure in igneous rocks?
"Geology"
James Geikie
As now used by road builders, it embraces a large variety of igneous rocks, chiefly those of fine crystalline structure and of dark-blue, gray, and green colors.
"The Future of Road-making in America"
Archer Butler Hulbert
The matter ejected has been estimated as twice the volume of Mount Hecla, or one hundred thousand millions cubic yards, probably as large as any single mass of the older igneous rocks known to exist-according to Bischoff, greater than the bulk of Mount Blanc.
"A Girl's Ride in Iceland"
Ethel Brilliana Alec-Tweedie