Composition and Constitution of Magmas

Abstract

The evidence upon which it is believed that a large number of the rocks of the earth’s crust are of igneous origin has been briefly detailed on page 11. The original molten rock matter is conveniently termed magma. Etymologically magma means a thick, pasty, porridge-like mass, and it is, therefore, entirely appropriate as applied to viscous molten material carrying crystals in process of formation. Present-day lavas, especially the molten lakes such as that of Halemaumau in Hawaii, are the most accessible and easily-studied representatives of magmas.