Geological Observations On Volcanic Islands

The overlying basaltic lava is in some parts extremely vesicular, in others little so; it is of a black colour, but sometimes contains crystals of glassy feldspar, and seldom much olivine. These streams appear to have possessed singularly little fluidity; their side walls and lower ends being very steep, and even as much as between twenty and thirty feet in height. Their surface is extraordinarily rugged, and from a short distance appears as if studded with small craters.Darwin, Charles is the author of 'Geological Observations On Volcanic Islands' with ISBN 9781419121555 and ISBN 1419121553.