Abstract
Amygdale minerals in the Tertiary basalt lavas of eastern Iceland have a well-marked zonal distribution; the flat-lying zones mapped in the field bear no relationship to the lava stratigraphy and are inferred to be approximately parallel to the original top of the lava pile. An independent method of deducing the position of this is available, depending on the fact that the intensity of the Tertiary dike swarm in the area everywhere diminishes upward; extrapolation gives the altitude of zero intensity, which is in good agreement with the altitude of the original top of the lavas deduced from the mineral zones. Both support the observation that the lavas thin up-dip, and the implications of this on the interpretation of the structure and geology of Iceland are discussed.
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