AbstractThe distribution of eleven different patterns of magnetic anomalies over the maps is shown. The individual patterns overlying the land are correlated with the underlying geology, and on the basis of this correlation a geological interpretation of the sea areas of the aeromagnetic survey is proposed. The outcrops of crystalline rocks are largely confined to the present land areas, so that in most places the sea floor is composed of Devonian or younger rocks. The Newer Granites are classified into three types based on their magnetic properties. The Great Glen fault passes through Shetland where it causes a 65 km dextral displacement of the Devonian rocks and an unknown but possibly much larger displacement of the older rocks.