Summary of site:
In the study of layered rocks (stratigraphy) it is essential to subdivide the enormous thicknesses into convenient and identifiable units by using obvious characteristics, such as their fossil content or their appearance. This allows the rocks to be recognised and mapped over large areas. Within the major periods the largest divisions are called groups; a group is divided into formations which in turn are further subdivided into members. All are given names that either describe their appearance or, more usually, relate to the geography of the area in which they are found.
The Dromore Sandstone Member is the lowest division of the Mullaghmore Sandstone Formation which, in turn, is part of the Tyrone Group of Carboniferous rocks.
The Dromore Sandstone is only rarely seen through its cover of glacial debris but at the quarry in Dromore Big townland is the finest, most complete and typical section of this member known. Such sections are used as the yardsticks of comparison for all other outcrops of the same member and are given the special status of ‘stratotype’. The Dromore Big quarry is the stratotype for the Dromore Sandstone Member and should therefore be protected for future scientific reference.
Some 10m of bedded sandstones are seen in the quarry where they rest without interruption on the Bundoran Shale. At the base, the thin beds are formed of fine sand, normally stained brown; both bed thickness and grain size increase towards the top, where the colour fades to pale grey and almost white. The top bed is 85cm thick and contains a significant proportion of feldspar grains mixed with the quartz. A few sedimentary structures, such as cross lamination and parallel laminations, suggest shallow water but there are no ripple marks to indicate surface or tidal conditions. Fossils are limited to thin slivers of carbonised wood and the feeding traces and burrows of invertebrate animals that lived on and in the sand.
These rocks are about 345 million years old and were part of a sand flat that inundated the muddy seabed (now the Bundoran Shale) at a time of rapid shallowing. The wood fragments suggest close proximity to a coast and the clean nature and coarse grain size of the sand suggest rapid transport. The survival of feldspar grains in the upper beds is a clear indication of rapid burial; in normal circumstances it quickly breaks down into quartz grains and clay minerals. Conditions at the time were tropical, as the area drifted northwards across the equator on the fringe of a continent called Laurentia.
Following Dromore Sandstone times the sea shallowed further and the area became intertidal and, for a time, little sediment was transported in. In these circumstances the coastline baked under a relentless sun as the basal beds of the overlying Mullaghmore Sandstone show.
The threats are those usual to disused quarries.