The most complete succession of Carboniferous rocks found in Co. Limerick crops out in the Limerick basin, which is situated between Limerick and Tipperary. The zonal ranges of the chief lithological divisions of the Lower Carboniferous rocks have been determined, and two volcanic episodes, represented by the Lower and the Upper Volcanic Groups, are now known to have occurred early in S1 and early in D1 times. The porphyritic pyroxenes have been isolated from representatives of the lower group, which ‘constitute a graded series of olivine-basalts, trachybasalts, trachyandesites and trachytes, comparable with the Lower Carboniferous Scottish suite. Among the olivine-basalts, all the Scottish types have been recognised, with the exception of Craiglockhart type and mugearite.