| The geological mapping of the Carboniferous rocks in Subarea-1 has been completed by the Geological Survey of Northern Ireland. The information is published on the following geological maps:|
| GSNI, 1982. 1:50,000 Solid Geology of Sheet 45 (Enniskillen) GSNI, 1991. 1:50,000 Solid Geology of Sheet 44, 56 and 43 (Derrygonnelly & Marble Arch) GSNI, 1995. 1:50,000 Solid Geology of Sheet 57 and part of 58 (Lisnaskea) - in preparation.|
| The southwestern shore of Lower Lough Erne lies just outside the northwest corner of Sheet 44, 56 and 43 and is included on the 1:50,000 geological map of the Kesh area.|
| GSNI, 1994. 1:50,000 Solid Geology of Sheet 32 and 31 (Kesh).|
| All of the formations that constitute the Tyrone Group were erected by Oswald (1955) in the area between the Ox Mountains and Donegal Bay, in NW Ireland. In so doing he did not select strato- type sections but the geographical name of each formation offers sufficient clues as to the location of their best and most typical sections. Sites selected for these formations in Subarea-1 therefore represent a locality or localities where typical lithologies are displayed and, if possible, where diagnostic fossils may be collected.|
| New members, that occur within formations of the Tyrone Group in Subarea-1, are only recognised in the Dartry Limestone Formation. Stratotype sections selected by the GSNI for each member are thus accorded ASSI status and are described herein.|
| Within the Leitrim Group all the formations and members recognised in NW Ireland were erected by Brandon (1968, 1972) at stratotype sections in Cos. Cavan and Leitrim. The exceptions are the Glenade (Beds) Sandstone Formation (Oswald, 1955) and the Meenymore (Member) Formation, which West, Brandon and Smith (1968) included as part of the now obsolete Aghagrania Formation.|
| Each formation, and constituent members, and the selected ASSI are thus described sequentially commencing with the oldest unit. Although the lowest Carboniferous beds, the Basal Clastics, are considered to occur in this area, they are not exposed and therefore will not be described here.|
| This subarea is noteworthy for the occurrence (inter alia) of one of only two known exposures of Waulsortian Limestone in Northern Ireland, a fact which was not recognised until recently and which is recorded here for the first time.|
| I - TYRONE GROUP
In County Fermanagh the Tyrone Group comprises six formations consisting mainly of limestones and shales which overlie an unnamed and unexposed, in Subarea-1, basal sequence of dominantly clastic rocks that were deposited in terrestrial, peritidal and shallow marine environments. The sequence is concealed by drift deposits on the SW shore of Lower Lough Erne but is well exposed in the Clogher Valley. The basal beds were proven in deep boreholes drilled at Big Dog (1965), Slisgarrow (1984) and Kilcoo Cross (1985). The stratigraphy of these boreholes and detailed information on the basal beds is summarised in Philcox et al. (1992).
(i) BALLYSHANNON LIMESTONE FORMATION
Oswald (1955) included the basal conglomerate and sandstones within the Ballyshannon Limestone but these were removed by Brunton and Mason (1979) and the formation name restricted only to the limestones. The formation crops out along the SW side of Lower Lough Erne and supposedly extends southeastwards under Upper Lough Erne although exposure is limited to few localities.
The main formation outcrop occurs however in the Derrygonnelly area and several quarries, which expose the lower levels, but not the base, are developed near Blaney at the base of the north and NE facing escarpment. On higher ground to the SW of the quarries, successive strike-parallel SE trending ridges, with karstic features, expose the highest beds of limestone below the over- lying Bundoran Shale Formation. Typically the top beds of limestone form long southwesterly inclined dip slopes covered by a thin, patchy mantle of till and the outcrop of the Bundoran Shale may be identified by the appearance, and development, of till drumlins and ridges on that lithology, in preference to the relatively drift-free limestone terrain. The precise contact between the Ballyshannon and Bundoran formation is apparently not exposed but the highest limestone bed encountered in the area, at Inisway Townland (H1628 5184), is a foraminifera-rich grainstone and differs completely from the normal medium-grained packstones. As in the Kesh-Omagh area lithologies at the top of the Ballyshannon Formation in Subarea-1 record an episode of bathymetric shallowing which resulted, in the former area, in partial exposure and erosion and widespread micritisation and instigated, in the latter area, a change from open shelf to high energy shallow water.
In the Big Dog Borehole the formation is 345m thick whereas between Blaney (H165 528) and Roosky (H185 498) it is an estimated 200m.
Microfaunas recovered from the Ballyshannon Limestone indicate a late Chadian age for the basal part of the formation and an Arundian age for the upper part.
In the Blaney-Roosky area the Ballyshannon Limestone is divided into three informal members.
For site specific information see;
Key Site 174 - Blaney Quarry Key Site 175 - Carrickreagh Quarry Key Site 176 - Inisway Quarry Key Site 177 - Bellanaleck Quarry.
(ii) BUNDORAN SHALE FORMATION
This formation, described by Oswald (1955), is spectacularly exposed on the west coast of Ireland at Bundoran. In Co. Fermanagh the formation is rarely well exposed and its outcrop tends to be confined to low, drift-covered ground, sandwiched between the harder limestones of the Ballyshannon Formation below and succeeding sandstones of the Mullaghmore Formation. In Subarea-1 the principal outcrop occupies much of the alluvium- covered land adjacent to Lough Macnean Lower and west of Upper Lough Erne.
The formation consists of dark grey, calcareous mudstone with thin limestones and yields of rich macrofauna dominated by solitary and rugose corals and by large brachiopods. Limestone beds are usually thin and lenticular and may be derived by turbidite flow. They frequently contain the concentrated debris of crinoid ossicles, broken bryozoa, brachiopods and corals and, an abundant microbiota including archaediscid foraminifera such as Paraarchaediscus at the involutus stage which indicates a mid to late Arundian age.
Of all the formations in the Tyrone Group the Bundoran shale is one of the few that maintains its lithological integrity over much of Northern Ireland and significant variations are usually confined to a thin sandstone member at, or just above, the formation base. The deposition of the shales seems to have accompanied an episode of marine transgression northwards and eastwards onto metamorphic rocks in the Southern Sperrin Mountains and along the north side of the Down-Longford Lower Palaeozoic massif. Its thickness is extremely variable ranging from 555m in the Big Dog Borehole, to 438m and 427m at the Kilcoo Cross and Slisgarrow boreholes, to a minimum of 60m in the area north of Derrygonnelly.
At the top of the Bundoran Formation the fossiliferous shales and thin limestones are gradually replaced by siltstones, very fine sandy siltstones, heterolithic siltstones and sandstones and finally by dark grey fine-grained silty sandstones. These changes record the progressive influence of deltaic sedimentation on the basin and herald the regional influence of increased erosion and uplift of the hinterland leading to the deposition of the Mullaghmore Sandstone Formation.
For site specific information see;
Key Site 178 - Claragh Townland.
(iii) MULLAGHMORE SANDSTONE FORMATION
The Mullaghmore Sandstone was described by Oswald (1955) from coastal exposures west of the Ox Mountains in NW Ireland. It is stratigraphically bounded by the Bundoran Shale Formation below and Benbulben Shale Formation above. Mullaghmore Head, 10km west of Bundoran, is the type locality. Shales within this section have yielded a rich miospore assemblage of the TS Biozone and are assigned a late Arundian to mid-Holkerian age (Higgs, 1984) although Buckman (1992) whilst studying the trace fossils in the sandstone there, reiterated the erroneous correlation of the Mullaghmore Formation and the Holkerian Stage, in its entirety.
The sandstones of the Mullaghmore Formation were derived by uplift and erosion of land located to the north of Subarea-1, in Co. Fermanagh. Its geometry in the basin is a wedge that thins to the south from a source in the northwest and northeast. Analysis of the diverse ichnofauna and sedimentary structures by Buckman (op. cit.) are indicative of a shallow water marine environment.
In Subarea-1 despite the extension of the formation outcrop south from Derrygonnelly to the eastern end of Lough Macnean Lower, the existence of these rocks south of a west-trending fault at Drumscollop (H140 482) is unproven. Numerous exposures do occur however in the formation outcrop east of Lough Melvin, in the Ninny's Hill area (G985 565) and in the district between Derrygonnelly (H12 52) and Monea (H15 49) 5km to the southeast. The selection of a single site that is representative of the Mullaghmore Formation in Subarea-1 is therefore somewhat problematical but a locality near Derrygonnelly has been chosen.
When unweathered, the sandstones are typically grey, fine- to medium-grained, moderately well-sorted and calcareous, and they are in beds up to 0.3m thick. Bedding surfaces are commonly rippled and bioturbated. Most surface exposures of these rocks are deeply weathered however and consequently are stained by an orange-brown crust on the buff to white decalcified sandstone. Coarsening-upwards cycles consist of fine-grained sandstones with parallel and convolute laminations, and ripples and grey siltstones at the base, succeeded by medium-grained, well-sorted cross-laminated subarkosic sandstones with coarse bioclastic sandstones at the top. The bioclasts include brachiopods, gastropods, nautiloids, bivalves and crinoid ossicles with pellets and radial-spar ooliths. Based on this lithological variation the environment of deposition seems to shift from a prodelta location to a more proximal sandflat situation. Periodic incursions of brackish to fully marine conditions occurred periodically and introduced a marine benthos to the delta top.
The thickness of the formation varies from about 200m at the type locality to 204m in the Slisgarrow Borehole and 217m at Kilcoo Cross, both in Subarea-1. The base of the formation is not exposed in this subarea and only at one locality (Key Site 179) is the conformable transition with the overlying Benbulben Shale Formation exposed.
For site specific information see;
Key Site 179 - Derrygonnelly Road Cutting.
(iv) BENBULBEN SHALE FORMATION
This formation was described by Oswald (1955) from outcrops in Co. Sligo and its type area is located there in the Benbulben Range and the Dartry Mountains. In Subarea-1, in Co. Fermanagh, its outcrop mostly occupies low-lying drift covered ground thus limiting exposure to deeply incised streams. Nevertheless in a few places, in particular on the north side of Cuilcagh Mountain, the SE face of Belmore Mountain and NW of the Glen Syncline to the NE of Garrison, there are extensive exposures demonstrating the lithological uniformity of the Formation. The Benbulben Shale is lithologically similar to the Bundoran Shale Formation but is darker coloured, often less calcareous but more fossiliferous. Its thickness is highly variable, ranging from 365m in the Slisgarrow Borehole (H026 518), to 317m at Big Dog (H019 497) and 198m at Kilcoo Cross (G970 481). At outcrop its thickness is consistently less than that recorded in boreholes, ranging from ~150m in the area SE of Belmore Mountain to 90m at Derrygonnelly.
The formation consists primarily of dark grey, almost black, calcareous fissile shales with interbedded thin, nodular bioclastic limestones and lenticular sandstones. Philcox et al. (1992) identified substantial lateral interfingering between shales of the Benbulben Formation and limestones of the succeeding Glencar Formation in wireline logs from the deep boreholes. They demonstrated that the relatively thin succession in Macnean-2 is laterally equivalent to only the lower half of the much thicker sequence in Slisgarrow-1 where, in the top of the shale, there are several distinct limestone tongues up to 6m thick which correlate with similar thick limestones in the base of the Glencar Formation in the Kilcoo Cross Borehole.
In the Northwest Basin the Benbulben Shale, like the Bundoran Shale, maintains its uniform lithology over the entire region and shows no significant variations on the dominant mudstone - thin limestone character. The deposition of the shales was accompanied by a cessation of sand entering the basin, uniform rate of subsidence and a transgression, and bathymetric deepening, of the sea over former delta complexes of the Mullaghmore Sandstone.
All lithologies are extremely fossiliferous. The mudstones in particular contain abundant remains of fenestellid bryozoa and brachiopods but it is the large specimens of the solitary coral Siphonophyllia benburbensis and, to a lesser extent of fragmented colonies of various species of Siphonodendron that is so characteristic. This formation also contains the first occurrence of the compound coral Lithostrotion, which in many localities are inverted and show evidence of transport. Limestones, though thin and often lenticular, commonly contain a graded transported assemblage of bioclast fragments, in particular crinoid ossicles and may reflect an origin as tempestites or from turbidity currents. Thin sandstone beds are usually channelised and erode the underlying mudstone indicating sediment flow from distant shallow water and land areas.
Foraminifera are particularly important in defining the precise age of this formation especially at its base. The occurrence of involutus stage paraarchaediscids and Uralodiscus, some 4m above the formation base, in the Kesh-Omagh area indicates a mid- to late-Arundian age. Higher in the formation there are records of concavus stage archaediscids and Archaediscus sp, both Holkerian entries and Endothyra archerbecki, together with a profusion of relatively primitive archaediscids, which reflects a position within the early Asbian.
Sites, exposing the Benbulben Shale Formation, which are selected for ASSI status occur in the Lough Macnean Lower part of Subarea-1 and demonstrate lithologies and macrofauna typical of the formation (Site 180) in one case and its conformable upper contact with the succeeding Glencar Limestone Formation at the other (Site 181). The formation base and conformable lower contact are described in the section for the Mullaghmore Sandstone Formation under Key Site 179.
For site specific information see;
Key Site 180 - Rahallan Townland Key Site 181 - Tullyhona stream.|
| (v) GLENCAR LIMESTONE FORMATION|
|This formation, described by Oswald (1955), consists of alternating argillaceous limestones and shales, the limestones occurring in a greater proportion than the shales. The Type Area is in the western Dartry Mountains in Co. Sligo and the boundary with the underlying Benbulben Shale is gradational up over a 3m interval from a shale dominant to a limestone dominant sequence.|
|In Subarea-1 in Co. Fermanagh the distribution of this formation follows closely the outcrop of the Benbulben Shale Formation, flanking the upland areas of Belmore Mountain and Lough Navar Forest in the north and the Lough Macnean Valley and Cuilcagh Mountain in the south of the area. The typical lithology is well bedded, commonly cherty limestones and thin to thick calcareous splintery shales. The formation thickness is highly variable ranging from 171m in the Kilcoo Cross Borehole to just 18m in the Big Dog and Slisgarrow boreholes and 40m on the north side of Cuilcagh Mountain where the Tullyhona section (Site 181) completely exposes the formation.|
|The upper contact of the Glencar Limestone and the succeeding Dartry Limestone Formation is frequently exposed and, although extremely variable, is almost always clearly defined, very often near the base of limestone cliff sections. The contact between the formations may be seen at the following localities:|
|1. Hanging Rock (H111 364) Contact is between interbedded limestones and shales and the base of a micrite mound comprising unbedded limestones. The contact is variable, in places conformable, at others it is erosional, laterally gradational and interfingering and probably diachronous. 2. Southeast Belmore Mountain (H154 412) A lenticular micrite mass forming the main cliff occurs in the top of the Glencar Limestone and although formed of unbedded (Dartry Limestone-type) micrites is succeeded by bedded lithologies of the Glencar Limestone. 3. Magho Cliffs (H08 57) The Glencar Limestone forms the middle, vertical, portion of these cliffs south of Lower Lough Erne and is about 170m thick. While the lower half of the formation and the contact with the Benbulben Shale is concealed by block scree, above the 150m contour there is almost complete exposure. The contact with the Dartry Limestone occurs at about 230m O.D. and the latter comprises bedded cherty limestones.|
|The Glencar Limestone contains a coral-brachiopod fauna of Asbian age. Unusually for the Lower Carboniferous of N. Ireland some elements of this fauna, notably the brachiopods and bryozoa, are silicified and superbly preserved specimens may be released from the limestone by solution in dilute acid. In the north of the area at Drumreask (H100 567) and at the eastern end of Bunnahone Lough (H105 550) exceptional collections of brachipods (Brunton, 1966) and bryozoa (Taverner-Smith, 1973) were obtained from the limestones. Because of the proliferation of bryozoa, foraminifera are not common in the limestones although an assemblage recorded from Bunnahone Lough contains Archaediscus stage angulatus indicating an Asbian age or younger.|
|For site specific information see;|
| Key Site 181 - Tullyhona stream Key Site 182 - Cladagh River, Marble Arch.|
|(vi) DARTRY LIMESTONE FORMATION|
|The formation was established by Oswald (1955) in NW Ireland where the Type Area is on higher parts of the Benbulben Range and Dartry Mountains. He noted the occurrence of two main lithologies; bedded cherty limestones which envelop what he termed, "reef limestones". In Subarea-1, in Co. Fermanagh, the Dartry Limestone Formation consists primarily of the bedded limestones with partings of splintery shale and the KNOCKMORE LIMESTONE MEMBER, which is equivalent to Oswald's "reef limestones". In the upper part of the formation on Belmore Mountain and north and east of Cuilcagh Mountain, 4 additional members are distinguished. Of these the Carrickmacsparrow Limestone, Cloghan Hill Limestone and Cloghany Limestone are confined to this part of Subarea-1. The Carn Limestone Member was first referred to by Brunton and Mason (1979) but was regarded by them as a localised deposit at the base of the succeeding Meenymore Formation, the lowest unit of the Leitrim Group. Similarly Brandon (1977, p.7), without naming the strata, accurately described the alternation of limestones and shales, that is so characteristic of this member, at Polliniska (H165 290) and, although noting the faunal affinities of these beds with the Dartry Limestone Formation, included them in the Meenymore Fmn.
The thickness of the Dartry Limestone Formation is extremely variable and depends on the development or absence of mud mounds of the Knockmore Limestone Member. On the east face of Cuilcagh Mountain for example, where the Knockmore Limestone Member is not developed, the formation is about 130m thick. In contrast on the north side of Cuilcagh and on the south side of Belmore Mountain, the Knockmore Member constitutes a major part of the total 280- 300m thickness of the Dartry Formation.
The base of the Dartry Limestone is commonly exposed in Subarea-1 and the frequently complex and variable relationship with limestones of the Glencar Formation has already been discussed for that formation. The contact is always sharp but only demonstrably erosional at the base of the micrite mounds. The prograding diachronous fronts of the mounds may also be associated with the development of limestone conglomerates.
The Asbian age of the Dartry Formation is confirmed, not so much by its contained fauna but by the occurrence of Asbian ammonoids in both the overlying Meenymore and Bellavally formations. The formation contains an abundant, in places, macrofauna dominated by corals and brachiopods which although typically Asbian in character, cannot confidently be assigned to either the upper or lower part of the stage. A diverse microbiota contains fewer foraminifera than might be expected but the presence of angulatus stage para-and nodosarchaediscids and Vissariotaxis cf. compressa indicate an age no older than Asbian.
The sites selected for the Dartry Limestone Formation are not dedicated solely to that formation. In the north of Subarea-1 the Magho Cliffs (Site 186) expose superb, but often inaccessible, sections in the Benbulben Shale, Glencar Limestone and Dartry Limestone formations. In the southern part of Subarea-1 the eastern flank of Cuilcagh Mountain, extending from the border stream of Polliniska (H165 290) northwards to the southern edge of the Deer Park at Finlane (H165 330), is considered to be an area of outstanding geological interest, with a variety of karstic and speleological features. The stratotype sections for each of the new members, with the exception of the Carn Member, within the Dartry Formation are described in Key Sites 191, 192 and 193. The Dartry Limestone is exposed in small quarries (H169 301) on the east face of Cuilcagh Mountain.
Over a greater part of Subarea-1 the top bed of the bedded cherty limestones of the Dartry Formation is coral-rich, being packed with in situ colonies of Siphonodendron irregulare and is up to 1m thick. This bed is particularly well exposed on the east side of Cuilcagh Mountain between Finlane and Gortalughany.
For site specific information see;
Key Site 186 - Magho Cliffs Key Site 187 - Cashel Quarry.
(1) KNOCKMORE LIMESTONE MEMBER
See; Key Site 188 - Knockmore Cliff.
(2) CLOGHAN HILL LIMESTONE MEMBER
See; Key Site 191 - Cloghan Hill.
(3) CARRICKMACSPARROW LIMESTONE MEMBER
See; Key Site 192 - Carrickmacsparrow Townland.
(4) CLOGHANY LIMESTONE MEMBER
See; Key Site 193 - Cloghany Pothole, Beighy Townland.
(5) CARN LIMESTONE MEMBER
See; Key Site 194 - Aghatirourke townland caves, east Cuilcagh.
II - LEITRIM GROUP
The distribution of the various formations of the Leitrim Group in N. Ireland, and in Subarea-1, may be divided into 2 main groups. Distributed most widely is the group comprising the Meenymore and Glenade Sandstone formations and although the latter unit is restricted, in N. Ireland, to Co. Fermanagh, the former occurs in Fermanagh and extends eastwards into Co. Tyrone. In contrast, the outcrop of the standard formations erected by Brandon (1968, 1972), between, and including, the Bellavally Formation and Dergvone Shale Formation is confined to 2 areas, namely the Doagh Outlier, near Derrygonnelly, and the northern part of the Cuilcagh Mountains. Formations occurring above the Dergvone Shale in N. Ireland only outcrop on Cuilcagh Mountain.
No sites in the Doagh outlier are nominated as ASSI at present, with the exception of Site 200 for the Doagh Limestone Member of the Carraun Shale Formation, which is restricted to this area.
Because the Cuilcagh Mountains offer the most spectacular, in many instances, unique exposures of most parts of the Leitrim Group succession in N. Ireland it is proposed to nominate that whole area as an ASSI. Detailed 1:10,560 scale geological maps of Cuilcagh Mountain are held by the GSNI.
In N. Ireland the outcrop of the Meenymore Formation covers by far the greatest area of any of the units in the Leitrim Group and it is proposed to nominate 1 locality in Subarea-1 where lithologies typical of that formation are present. For all other units of the Leitrim Group present in N. Ireland, they are represented at outcrop on Cuilcagh Mountain, Key Site 20.
(i) MEENYMORE FORMATION
Oswald (1955, p.180) was the first to recognise a major, but usually poorly exposed, shale formation between the Dartry Limestone and the Glenade Sandstone formations in NW Ireland. Previous workers had forced the Geological Survey's standard divisions (Symes & Wilkinson, 1886) on all Carboniferous rocks regardless of local variations with the result that if the shale formation contained thin sandstones then it was assigned to the Yoredale Sandstone and if it contained thin limestones then the shale was placed in the Upper Limestone. As late as 1953 Padget still used this classification and did not recognise the shale formation.
This dominantly shallow-water shale formation is now called the Meenymore Formation and takes its name from a townland in Co. Leitrim on the NW side of the Lackagh Hills. The stratotype section is still located however at Aghagrania, Co. Leitrim 3.5km NE of Drumshanbo, where it is completely exposed (Brandon, 1977).
The Meenymore Formation is the only one in the Leitrim Group where considerable difficulties arise in correlation between different areas or even within one area. Faunal bands, evaporite beds and distinctive stratigraphical sequences are all discontinuous laterally and it is evident that water depths fluctuated in a quite haphazard manner across the vast area in which deposition of this very variable formation occurred. This variation is hardly surprising in view of the fact that the late Asbian in N. Ireland was a time of considerable tectonic activity. Products of this activity include huge local variations in the thickness of this formation and the contemporaneous development of at least 2 deep, non-marine basins on the southern and northern flanks of the Fintona Block. In contrast later formations in the Leitrim Group were deposited in a basin-wide, regular and predictable, cyclical sequence that bears little evidence of contemporaneous tectonism.
The age of the Meenymore Formation is based on the occurrence of goniatites. Assemblages include the following forms which indicate a B2 Zone age (Riley, 1990) and a position within the B2a Subzone (late Asbian).
Beyrichoceras Bollandoceras micronotum Entogonites sp. Girtyoceras sp. Goniatites maximus group Nomismoceras vittigerum
In the faulted block at Glennasheevar (H039 531) the lower part of the Meenymore Formation is exposed in the east-flowing tributary of the Sillees River, south of the Garrison-Carrick Lough road. In addition to medium grey shales and mudstones with occasional crinoid ossicles, brachiopods and solitary corals, the section exposes laminated algal limestones and rare micrites. At localities in this stream (H035 532) and in the stream (H041 528) draining northeast from Lough Naman, Gardiner and Mason (1974) obtained numerous specimens of the palaeoniscid fish Elonichthys serratus from a bed of black micrite 0.15-0.2m thick.
In N. Ireland and in Subarea-1 the Meenymore Formation is widely distributed. In the Lurgan River section, Key Site 198, the formation is ~50m thick and its upper contact with the Glenade Sandstone Formation is exposed. The precise base of the formation is however not exposed but an isolated exposure of the Carn Limestone Member (the only occurrence on the south side of Belmore Mountain) places a limit on the outcrop width of the formation in this area.
Based on the present outcrop of this formation the tidal flat area on which the varied sediments accumulated covered an area, in the north of Ireland, of at least 5000 square kilometres and was almost certainly much more extensive.
For site specific information see;
Key Site 198 - Lurgan River, Mullylusty Townland Key Site 20 - Cuilcagh Mountains.
(ii) CARRAUN SHALE FORMATION
In addition to the main outcrop of the Carraun Shale Formation on Cuilcagh Mountain, the formation is also present, in its entirety, in the Doagh Outlier, 6km west of Derrygonnelly. There the formation thickness is estimated at 160m (Brandon, 1972), compared to 51m on Cuilcagh Mountain, with this difference being largely accounted for by a 5 fold increase in the thickness of the shales, with thin limestones, located stratigraphically between the formation base (Derreens Limestone Member) and the Doagh Limestone Member (equivalent to the Tawnyunshinagh Limestone Member on Cuilcagh Mountain).
During the first geological survey of the Derrygonnelly area in 1886, the distinctive Doagh Limestone Member was misidentified as the Upper Limestone, equivalent to the Dartry Limestone Formation. The lithostratigraphical succession in the Doagh Outlier was correctly determined by Brandon (op. cit.) who recognised the Leitrim Group affinities of the rocks, defined the Doagh Limestone Member and correlated it with the Tawnyunshinagh Member.
For site specific information see;
Key Site 200 - Doagh Glebe Townland Quarries. ------------------------------------------------------------------ For more information on the Carboniferous System in N. Ireland see; Key Site 1171 - The Carboniferous System in N. Ireland - Introduction. Key Site 1172 - Carboniferous Biostratigraphy - Overview. Key Site 1173 - Carboniferous Palaeogeography of N. Ireland.|