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Earth Science Conservation Review
| Devlin’ Quarry, Moneymore – Clay-with-Flints |
| Site number: | 1303 | ||
| Locality Type: | Status: | ESCR | |
| Grid Reference: | H87158155 | ||
| Google maps: | 54.67451,-6.64983 | ||
| County: | Council area: | Mid Ulster District Council | |
| Period: | Cretaceous, Tertiary | ||
| Site Description | |
|---|---|
| Introduction: | |
Since chalk extraction ceased, the quarry has been used for the disposal of building debris and waste soil. Much of this material, which is now vegetated, was deposited in the northern part of the quarry where most of the chalk face is concealed, up to a level just below the base of the Clay-with-Flints (Photograph 12). Small amounts of fresh inert material are still being dumped and levelled in this part of the quarry. The full height of the southern quarry face is still exposed as no dumping has occurred in this part of the quarry. | |
| Description: | |
Site Geology: Ulster White Limestone Formation: Chalk of the Late Cretaceous Ulster White Limestone Formation occupies the greater part of the quarry face on the east side of the site. According to Fletcher (1977), the Ulster White Limestone Formation in the Moneymore area of south Co Londonderry is represented by four members, namely the Portrush Chalk, Ballymagarry Chalk, Tanderagee Chalk and Port Calliagh Chalk members (Figures 2 and 3). These members belong to the Post-Larry Bane chalk and are of Late Campanian to Early Maastrichtian age. The basal beds of the chalk in this area, which appear to fall within the Portrush Chalk Member, overlie unconformably red-bed sedimentary rocks of the Triassic Sherwood Sandstone and Mercia Mudstone groups. The unconformity is not exposed in the quarry. Antrim Lava Group: The upper part of the quarry comprises about 6m of subhorizontal basalt lava flows of the Lower Basalt Formation of the Early Palaeogene Antrim Lava Group. Clay-with-Flints: The best and most accessible section in the Clay-with-Flints is found in the northern part of the quarry. Quaternary Deposits: Rock head in the quarry is overlain by a thin layer of glacial till (boulder clay). The Clay-with-Flints detail: The outcrop of the Clay-with-Flints in Devlin’s Quarry forms an important link between the deposit at Gibson’s Quarry, Portadown (Site 2), with its mixed volcaniclastic and volcanogenic origins and uncoloured flints, and the pyroclastic flow of the Donald’s Hill Ignimbrite Formation (DHIF) at Donald’s Hill (Site 4). The section of the Clay-with-Flints illustrated below is located in the northeast corner of the site (Photograph 13). Both of the sub-horizontal contacts with the chalk and the basalt lavas are exposed at the north end of the quarry. The Clay-with-Flints is about 1.9m thick at this section. However, a few metres north of this accessible section there is a 3m deep palaeosinkhole in the top surface of the chalk that is also filled by the Clay-with-Flints (Photograph 14). Between the measured section and the palaeo-sinkhole the thickness of Clay-with-Flints decreases gradually until, at the margins of the sinkhole, only about 10cm of Clay-with-Flints separates the chalk and basalt lava. It seems likely that the thinning of the Clay-with-Flints was influenced by the presence of a slight topographic rise towards the site of the palaeo-sinkhole. While the outcrop of the Clay-with-Flints can be traced southwards along the east face of the quarry much of it is either too dangerous to access or is concealed by thin soil and vegetation. In Devlin’s Quarry, the Clay-with-Flints consists of a white to pale grey, lapilli-rich clay matrix with numerous small to medium sized flint nodules that all have a thick white crust but internally are universally stained a deep reddish purple colour (Photograph 15). Based on the presence of lapilli it is suggested that there is a strong volcanogenic influence in the formation of the deposit at this locality. The deep purplish colouration is due to baking of the flints, a feature that is also characteristic of flints in the DHIF, which originated as an ignimbrite (pyroclastic flow) with temperatures in excess of 600ºC. Although located some 40km SSE of Donald’s Hill, it is postulated that at least part of the Clay-with-Flints in Devlin’s Quarry is an unsilicified extension of the pyroclastic flow that forms the DHIF. Petrogenesis: The Clay-with-Flints in Devlin’s Quarry has been studied in detail in order to obtain as much information as possible on its origins, the nature of the parental volcanicity and to assess any petrographical and geochemical differences that may be apparent between the three separate layers that make up the deposit (Figure 14). Geochemistry Two clay samples from the Clay-with-Flints in Devlin’s Quarry (Figure 14) were selected for major and selected trace element analysis. The lower sample came from the basal 0.10m of the deposit, just above the top surface of the chalk while the higher sample came from the main, middle layer containing the concentration of purple-red stained flints. Immobile element ratios from both samples plot on a Zr/TiO2 – Nb/Y discrimination diagram in the andesite field. Petrography This sample, from the lowest 10cm of the Clay-with-Flints in Devlin’s Quarry, shows a grey clay matrix with fine laminations, possibly a flow structure, and small dark red lapilli. In thin section the lapilli are rounded, completely opaque (probably due to the oxidation of their Fe component) and comprise up to 5% of the section. Small flints, up to 0.5mm in diameter are present and were derived from the flint regolith that covered the chalk surface. The matrix is composed of a pale brown cryptocrystalline intergrowth of quartz, clay minerals and disseminated opaque oxides possibly replacing primary vitric material. In detail, differences in the optical density of different parts of the matrix reveal what were probably primary glassy volcanogenic lithic fragments, some reaching several millimetres in size. The sample is cut by narrow veins of colourless, low birefringence zeolite. | |
| Conclusions: | |
The petrographic study confirms that the Clay-with-Flints in Devlin’s Quarry is a volcaniclastic deposit, possibly a lapilli tuff. Despite the pervasive alteration affecting all the constituents, there is evidently an underlying primary fragmental structure, possibly a vitric ash, in which very small lava fragments are also discernible. It is also believed that the intense colour staining of the majority of the flints in the deposit was caused by heat and that the Clay-with-Flints at this locality is an unsilicified extension of the DHIF. | |
| Notes: | |
The full series of Clay-with-Flints records is as follows: Record no. 1300 Introduction to Clay-with-Flints of Northern Ireland Record no. 1301 Belshaw’s Quarry – Clay-with-Flints Record no. 1302 Gibson’s Quarry, Portadown – Clay-with-Flints Record no. 1303 Devlin’ Quarry, Moneymore – Clay-with-Flints Record no. 1304 Glenshane Pass – Clay-with-Flints Record no. 1305 Donald’s Hill – Clay-with-Flints Record no. 1306 Tircrevan Burn – Clay-with-Flints Record no. 1307 Ballycastle – Clay-with-Flints Record no. 1308 Demesne Quarry, Glenarm – Clay-with-Flints Record no. 1309 Magheramorne Quarry, Larne – Clay-with-Flints Record no. 1310 Bellevue, Belfast, Co Antrim – Clay-with-Flints Record no. 1311 Soldierstown Quarry, Moira – Clay-with-Flints | |
| Keywords | |
|---|---|
| Rocks: | Chalk, Clay, Flint, Basalt |
| Access | |
|---|---|
| Approach: | Private land. Disused quarry (Photograph 12), Ballindrum Townland [Grid Ref: H8715 8155], 2.25 km SSE of Moneymore, Co. Londonderry (Figures 12 and 13). |
| Restrictions: | Private land |
| Record type: | ESCR report | ||
| Entered by: | I J Enlander | ||
| Last updated: | 28 Mar 2019 | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Devlin’ Quarry, Moneymore – Clay-with-Flints, County , site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=1303. Accessed on 2026-11-07. |
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