Abstract

The discovery that the Lackagh Quartzite correlates with the Ards (Errigal) Quartzite (Pitcher & Shackleton 1966) means that the structure in the meta-sediments adjacent to The Main Granite at Dunlewy, as deduced by Rickard (1962), is incorrect. Revision of the mapping (Fig. 1) shows that the structural arrangement can be interpreted in conformity with the new stratigraphical concept. All the formations of the Greeslough Succession (Fig. 1B) are attenuated in this district and the structure is complicated by the Dunlewy crossfolds (Rickard 1962). Several black pelitic layers were previously included in the Creeslough Formation but a consistent structural model can now be made by assigning these to the Ards Black Pelite Formation. Similarly the several limestone bands reduce to two main members, one within the Ards Pelites and the other close to the junction of the Ards and Greeslough Pelites—the latter representing the Altan Limestone Formation.

Southwest of Dunlewy Lough black pelites surround the outcrop of the Greeslough Pelites defining an anticline, on the southern flank of which the Ards Quartzite is reduced to a very narrow outcrop of flaggy quartzites, previously mapped as Lackagh. Within this quartzite an interlayered pelite and flaggy quartzite unit is now recognized (Fig. 1): this resembles the Falcarragh Pelite Formation at its closest outcrop to the north west. There must be a tight syncline here in which the intervening Clonmass Group has been sheared out, as elsewhere in the Dunlewy crossfolds (Rickard, 1962).

The structure that is now deduced is that of two

First Page Preview

First page PDF preview
You do not currently have access to this article.