Igneous rock types in engineering geology pdf download
these Plutonic rocks as the stratified division of the crystalline or hypo gene formations, and have stated that they differ from the volcanic rocks, not only by their more crystalline texture, but also by the absence of tuffs and breccia’s, which are the products of eruptions at the earth’s surface, whether thrown up into the air or the sea. They differ also by the absence of pores or cellular cavities, to which the expansion of the entangled gases gives rise in ordinary lava, never being scoriaceous or amygdaloidal, and never forming a porphyry with an uncrystalline base, nor alternating with tuffs. From these and other peculiarities it has been inferred that the granites have been formed at considerable depths in the earth, and have cooled and crystallized slowly under great pressure, where the contained gases could not expand. The volcanic rocks, on the contrary, although they also have risen up from below, have cooled from a melted state more rapidly upon or near the surface.The Plutonic rocks may be treated of next in order, as they are most nearly allied to the volcanic class already considered.