In his discussion of geosynclinal development in the Silurian of the British Isles, Ziegler (1970) distinguishes land masses, shelf deposits, turbidite deposits and graptolitic shales. He further distinguishes between blocks such as the Midland Block and Eocaledonia (where passage from shelf to turbidite facies is sharp and associated with major fractures) and tectonic lands such as Cockburnland or the Irish Sea Land Mass (where the shelf record is only in the form of slumped shelly deposits).
Ziegler extrapolates his palaeogeographic maps across Ireland—a slimly documented area. He tentatively places the shelly succession of the Dingle Peninsula as part of the southern margin of Eocaledonia, and asserts that the turbidites and associated deposits of the Central Inliers seem to be related to the northern (Eocaledonian) margin of the trough. A contrary view has been suggested by Holland (1969 p. 208) who thinks that the Irish Sea Land Mass might have contributed sediments from the east.
Ziegler's palaeogeographic maps (op. cir. Figs. 3–6) show the trough as asymmetric, with turbidites mainly confined to the north-western side and graptolitic shales to the south-east. The evidence for this palaeogeographic interpretation in Ireland is slender and his conclusions are presumably based on his interpretation of the geology of the Central Inliers.
As will be seen in the following account there are some points concerning these inliers which are worthy of mention although their explanation is by no means clear.
The inliers are thought to fall into two groups and the argument for this is