The volcanic rocks of Iceland have been grouped by Tyrrell and Peacock (1928) into:

3. The Recent, Post-Glacial and Late Interglacial Eruptives.

2. The Early Glacial Breccia or Palagonite Formation.

1. The Pre-Glacial Kainozoic Basalt Plateau.

Group 1 consists of nearly 10,000 feet of basalts with lignite beds, acid extrusives and acid and basic intrusions. In the east and west of Iceland the old plateau is exposed, but centrally it is down-faulted and covered with more recent tuffs and lavas.

Group 2 contains a varied assemblage of deposits comprising tuffs, breccias and lavas, moraines, boulder clays and fluvioglacial sediments (Nielsen and Noe-Nygaard, 1936 a). The lower part of this formation consists of over 2000 feet of basaltic lavas with interbedded glacial and fossiliferous deposits, and the upper part of glacial and fluvio-glacial deposits with doleritic lavas.

Group 3 is made up mainly of basaltic lavas but with occasional acid phases. In the ice-covered highlands the volcanoes have continued to produce tuffs and breccias.