Some Observations on the Antrim Basalts and Associated Dolerite Intrusions

The work embodies miscellaneous observations on the general structural characters of the Tertiary basalt lavas and minor intrusions of north-eastern Ireland. Individual lava flows are found to average twenty-two feet in thickness, the thickest reaching 150 feet. Certain flows can be traced horizontally for as much as six miles. Basalt pegmatites are described which bear sodalite, a mineral new to Ireland.Composite lava flows are recorded for the first time in Ireland. Several examples have been located, and in each the components, separated by a sharp but unchilled contact, are of olivine-basalt and picrite-basalt respectively. The lavas are associated with a swarm of dykes and one, possibly two, dykes are now known to be the feeders of lava flows. Dolerite plugs may also represent the feeders to lava flows.Six newly discovered plugs are recorded, bringing the total number known to around thirty. The Donegore dyke, formerly regarded as a broad dyke, is re-interpreted as a string of four small plugs.