The dominant geological features of Iceland are its glaciers and its volcanoes, both of which are developed on a tremendous scale and afford unusual opportunities for detailed study. The island itself is essentially an uplifted plateau country, averaging 500 to 700 meters in elevation, and consisting in large part of basaltic lava flows and associated tuffs and breccias. Fringing this plateau at different points are lowland coastal strips, whose total area is nearly one-fifteenth of that of the entire island; to these all habitation is practically confined, the rest of the island being a barren waste of lava and glacial debris, devoid of forests, and even vegetation, and worthless from an economic standpoint, but valuable to the geologist because of its excellent exposures.
Soundings by the Danish government have shown that these lowland coastal areas, in north and west Iceland especially, extend seaward as a coastal rock shelf 100 . . .