15. Mountain Landscape.
29th August 2011
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“A small pinnacle of ancient rock breaking off from a Sandstone escarpment on the flanks of The Playbank overlooking Lough Allen in north west Ireland. The small cap of Ferns and earth survives here as it is protected from grazing. This cliff was, in all probability, formed during Ireland’s last Ice Age long before man settled on this Island.”


This report is on a trip into the hills over the north-east corner of Lough Allen. The hills would have the common name of The Playbank. Bencroy is to the south, and Slieve Anierin lies further south. Cuilcagh mountain is about 10km to the east. The purpose of the trip was to explore another area of Lough Allen Basin that we haven't previously investigated. It is a moorland area with a lot of heaths and heathers, but different to the raised bog reported in TALA 13.

It is an area we haven’t reported on before. Work at LoughAllenBasin.com is very much scheduled by the weather and by the seasons and by our availability. In the early Spring, it is a full time occupation trying to record, photograph, and count, the number of birds breeding on the islands and the distribution and the success of the breeding. This is followed shortly afterwards by the plants and particularly the Spiranthes orchids where, at this stage, our survey is just coming to an end.

The walk was from Carntullagh up to Cloghasaggert, then west to the Playbank, back along the cliff edge, and back to Carntullagh. Access is a by a straight mountain road followed by a track running in a north easterly direction directly into the mountain. This comes off the Ballinaglera to Bencroy mountain road 3km east of Ballinaglera. Conditions were good. Rain was promised, but it stayed dry for nearly the whole morning. Moderate wind, and overcast nearly all the time. Fairly good photographic weather, aside from slight problems with the wind.

Moorland & Raised Bog

This area can be categorised as moorland on upland sandstone and shale bedrocks. The raised bogs tend to be at a lower altitude and form in flat ground where water remained after the last glaciation. They are similar in ways, but also very different. Similarities would include things like the Calluna vulgaris, Common Heather, which is widespread in both areas. But the Bell Heather and the Cross-leaved Heather are different. For most of the mountain area covered the Cross-leafed Heather is not present. It has been replaced by Bell Heather and the Cross-leaved Heather disappears at 300 to 400m altitude.

Part of the purpose of this project has been to investigate the occurence of the Bell Heather, and to take photographs. We have heard reports of Bell Heather in the raised bog, but we have not come across it in lowland raised bogs in this area. There are also many variations in other plant species present (the smaller, infrequent, interesting plant species present). Most of this work was on plants and landscape, though interesting numbers and behaviour was observed in flocks of Mistle Thrushes — which is not a bird you would associate with bare mountains.

A deep crevice at the edge of a Sandstone bed where ice has pulled the rock apart. The height shown here is about 3 m. with heathers and Bilberries at the top, ferns and mosses below.

Young scientist at work studying the Flora of this very specialised Habitat. It is important to record flora and fauna of an area at any particular time.

A view along the edge of this scar showing where whole areas of bedrock have been removed or pulled apart. A U-shaped glacial valley can be seen in the background.

Structure & Landscape




This is an upland area, part of an extensive region covered with a thin layer of blanket bog, which includes Cuilcagh mountain, Slieve Anierin and Bencroy, all on the east side of Lough Allen. The main area we studied was from 350m up to 500m in altitude. The hills are rounded, largely covered in turf. Turf has been worked in certain areas, but mostly the turf is very shallow, and lies mostly on sandstone and shale.

Two distinct features exist in this area and these are the elements that attracted us to survey the area. There are two scars running along the face of The Playbank and Benveg, roughly 50m above one another in altitude, both of them being about 10 – 15m high. This is exposed, dense Lackagh formation sandstone. These cliffs have apparently been caused by glaciation, and contain some interesting flora.

Above these cliffs, the mountains are smooth and heather-covered, and fairly easy to traverse. There are areas of wet ground in valleys here and there, and at the edge of bog cuttings. These are quite dangerous, are rich in sphagnum, and have been searched in previous times for the rare Bog Orchid. Unsuccessfully to date, as far as we know. To the east, in an area which was not visited on this day, there are three small lakes: Lough Nambrack, Altshallan Lough and Knockgorm Lough.

The geology and geomorphology of the area is quite simple but interesting, and relates largely to the ice age. This whole area is Upper Carboniferous — Namurian. The main area studied would be sandstone, but there are extensive areas of shale both above and below this sandstone. The rock is lying largely flat with a very gentle dip towards the south-west. The sandstone beds are thick and exposed at the edges where they have been eroded.

Briefly, the structure of the geology is that the top of the mountain is covered in Lackagh sandstone, thick inter-bedded fine sandstones and coarse siltstones mixed together. Above this is the Bencroy shales and the Bencroy sandstone member, but these are not present on The Playbank. Underneath the Lackagh sandstone formation is the Gowlan shale formation and the Dergvone shale formation, the latter reaching down to the shore of Lough Allen in places. These are major shale beds that are capped by the sandstone in this particular area.


Common Polypody surviving here on the tops of small tors and in crevices
where sheep can’t get to them...

The geomorphology of the area relates to the ice age and local glaciations that would have formed on The Playbank and other local mountains, but may have been very local. The movement of the ice is indicated by the tearing of the Lackagh sandstone where it forms cliffs. As the ice moved across the exposed sandstone it would have pulled by suction large sections of rock from the front of the exposed sandstone. This led to cracking and deep crevices forming in the rocks left behind. These are curved in places, and one can very visually see the effect of the ice. The ice at this point was heading south-westerly.

To the west of The Playbank it seems to veer west and head down towards Dowra. To the east of The Playbank, in the Benveg area, it would head east down towards Ballinamore. So, we're dealing with a watershed here. Where the ice moved to the east (i.e at the top of the picture), a deep U-shaped valley is visible. This is characteristic of landscape formed by ice.


A fantastic specimen of Fir Clubmoss from the crevices of The Playbank. Note the spores on the middle of the stems. This specimen was 12cm. high with the stiffness and rigidity of a small conifer — hence the name.


A crevice opening up on the edge of the Sandstone bed and the rock being forced south and east. You can just discern the start of the glacial valley in the distance. It was in these deep shaded areas that we found the Filmy Fern and the Clubmosses and other shade tolerant species like the Wood Sorrel and Bilberry.


The cracks in the Lackagh sandstone are the haunt of Filmy Fern and Fir Clubmoss. Quite interesting species which we have studied further below.

Studies of the Filmy Fern

A broad view of one of the walls of the crevice shown above, covered with one of our smallest ferns, the Filmy Fern.

These photographs are taken with flash (or amplification) in the dark places where they like to grow.

Bilberry struggling to survive in the softer bands of theSandstone. They do not seem to grow in the thicker Grit layers.

Other Species found in Crevices

Filmy Fern Fronds shown in more detail. These plants are not uncommon but only found in the particular conditions and niche that suits them... dark and wet with only occasional light.

The frond shown in this picture is no more than 5cm. long.

Fir Clubmoss and Filmy Fern on a ledge deep down in one of the crevices.

A microscopic examination of the tip of one of the fronds showing cell structure and a single vein reaching towards the end of the frond. This characteristic is used in identifying the two species of this fern that can occur.

Wood Sorrel is like Bilberry, primarily a plant of woodlands. It is not found on the mountain but is managing to survive in these deep shady clefts for millenia! Some Dryopteris Ferns
(BroadBuckler Fern) also appear here.

Our Trip

Main occupation of the day was the photography of plants. Some interesting species... which are listed as we came across them.

Firstly, the Bell Heather. This put in its appearance as we walked up through the lowland moorland into the forest and onto the lower scar. It was first noticed at about 400m, but may have occured lower down. Interestingly, up to that height the Cross-leaved Heather had been present, so the pink heather was rapidly replaced with the red heather, and the Cross-leaved Heather rapidly died out as we climbed higher. On the return trip, Bell Heather was seen at a lower altitude, down as far as 350m before it was replaced by the Cross-leaved Heather.

Another significant plant on both the lowland bog and the slopes at the top of the playbank would be Bilberry. In most place this was very low in height, though it did reach up to 70cm at the edge of forests. It was prolific, loaded with berries, and even the smallest of plants  — which had probably been kept short by sheep grazing  — were fruiting all over the mountain. An interesting survivor from times when this mountain would have been covered by woodland.

This is the Bell Heather (replacing the Cross-leaved here). A much deeper colour and a plant of the higher and drier hills. Was found on all the slopes and cliff edges of The Playbank

Heath Bedstraw was quite striking on this heath in among the Heather (Calluna vulgaris) and the Bell Heather, it was a striking and prolific patch of pure white 4 petalled flowers

Bog Asphodel was scarce here, flowering individually and much later than the specimens that are widespread on the Raised Bog. This specimen was at least a month behind lowland plants.

After walking up the hill, going through the forest, and along some of the moor, we came to the shattered and torn Lackagh sandstone formation, and immediately found suitable crevices where the Filmy Ferns were studied. Many photographs were taken and the defining characteristic  — one of them anyway —  is the length of the vein, and this is shown in the microphotograph above. There are two species of Filmy Ferns across the British Isles, one Hymenophyllum wilsonii and the other H. tunbrigense.

Plants of the Wetter areas...

This one puzzled us for a while.
These ‘flowers’ were common in the area but they are only Sphagnum carried up from the ground on a Rush!

A water-hole among the heather, attracts some water loving species — Ferns and Woodrush

More detail of the flowering heads of Jointed Rush growing in this wet area.

The Fir Clubmoss is also present in stunningly beautiful plants in these clefts and other shady places. Other plants would include the Bog Asphodel. This was probably most obvious for its scarcity. It is a very common plant in raised bogs. It was only infrequent on this blanket bog. Also scarce or absent were insectivorous plants (often found on nutrient poor substrates) such as Sundew which was very abundant on the lowland bog. No Orchids were seen. A courtesy look was paid for the Bog Orchid, but we didn’t have much anticipation of seeing it here. Whether it ever occured, or will occur, or will ever be found, we do not know  — but this is a habitat and a facies that has been described to us as being suitable for the species!




Heath Bedstraw is another common and attractive plant of the area.


Sphagnum spp. were present everywhere that conditions were wet enough to support it. This included most of the area apart from the cliff edges where the land was too dry. Bright green Sphagnum — large red Sphagnum.


A hedge of Bilberries formed by the prevailing wind. The brown wind torn stems are seen on the right whereas green leaves and fruit survive of the flattened top surface. (A milder form of erosion than the ice but still affecting the conditions plants endure.)



Apart from Ravens, the only significant wildlife seen would have been Mistle Thrushes. There was a flock of up to 20 Mistle Thrushes, which were very wild and which we assumed were recent migrants as they probably would not breed in this area. However, one bird seen bathing in a hole on top of the sandstone showed young plumage. So, these may be local birds dispersing and foraging in a different habitat. They are typically seen in the high ground in Leitrim and Roscommon at this time of year and we have assumed that they are migratory because they are not seen here earlier in the year, but they may be migratory just from local forested areas where they breed.

The pool shown here would probably be a ground out by geological processes — an iron stone forming in the Lackagh sandstone formation. The sandstone beds all along the cliff tops was heavily pitted, very much like what one finds in Limestone. But presumably the method of formation would be slightly different. Ironstones are common in this strata and the photograph below shows a fossilised ironstone that has rounded out the sandstone on which it lies. Deposition of Quartz through water leaking around the stone and into the bed has hardened the edge of the hole, and this has left the ironstone in place. Most of the ironstone is not in place. It has been eroded, has travelled down the rivers and can be found on the shore of Lough Allen.

The thrushes particularly seem to enjoy bathing in these very natural birdbaths. Around these high bluffs and tors and bathing areas, the bird droppings from the Mistle Thrushes are all purple indicating their main food source at the present. The presence of Bilberries in the area could well be the reason why thrushes migrate through this place.



A Weird and Wonderful piece of Natural Serendipity...


A migrating bird takes a Bath...

There were many Mistle Thrushes flocking in this upland area. Around these bathing places were many bright purple droppings; they had been feeding on Bilberries!

So, today, they come to an ancient place and enjoy a rich diet of fruit and wash it all down with a luxurious bath in a Bird Bath with a View! Can this be the reason why Mistle Thrushes migrate through these areas in the Autumn?

Erosion and Landscape Formation.

On the left we outline a rather quirky example of the way Geoloogy and Climate combine to form a landscape. In this case it is only a detail — and a rather trivial one — but it is the same processes in minature that on a large scale have created the shape and the character of Lough Allen and, indeed, Ireland as a country.

What is utterly fascinating about these upland areas of Leitrim and Sligo is the way so much of the prehistory of the formation of our land can be read comparatively easily. Two reasons contribute to this. The geology is largely quite simple. The beds are as they were laid down rarely having any significant folding. Mostly Upper Carboniferous non-limestone rocks in this area and Lower Carboniferous limestone rocks further north in Sligo.

The second feature is the accessibility of the evidence. In upland areas rocks are everywhere; this may not be the case lower down. Also, very large tracts of land in this region have had very little disturbance from mankind or other natural forces. The biggest player in the process of evoloution of the landscape in ‘recent’ times has been the Ice Age. In geological terms, just a fraction of a second ago; in human terms, well — long before we were here!

But sometimes looking at these features you can be struck by how recent they seem. That big stone on the side of the hill probably hasn’t moved since a glacier dropped it there 12,000 years ago. Similarly the iron nodules we find around Lough Allen have probaly lain there for millenia; they are too heavy to be moved by any forces other than ice or gravity!

And those scratches in the rock? They look like they were left by a mason maybe a hundred years ago. But they were actually left 1,000s of years before any stone builders ever lived in Ireland.

Enormous satisfaction and interest can be obtained from observing and thinking about such features... maybe there is scope for a New Naturalist Club in this area bringing together all of us who enjoy our birds, our plants, our fish, our moths... and (of course) the beautiful landscape and geology!



Spectacular Bathing place...

All along these high tors and cliffs are these perfectly made sandstone bird baths. They are hemispherical and quite deep, roughly 30cm. in diameter.

The birds can almost disappear in them, all that shows is a flurry of wings and water spraying. These Thrushes are very wild, not like ones you see in a park. They seem to enjoy the great view they have from these places and move on whenever anyone comes near.




300,000,000 Years ago...

But these aren’t Victorian Bird Baths. Picture on the left shows how they are formed. A heavier sphere of rock (ironstone) lodges in the sandtone. Then it is exposed and plucked from its nest by ice or other forces, leaving a perfectly hollowed out natural pool.

But this is Namuriam Sandstone from the Upper Carboniferous... That dates these structures as being c. 300 Million years old. Isn’t that neat!



The geology of the Lackagh sandstones was very interesting for the layering, its erosion by ice, the sharpness of the sand (or grit), and the presence of numerous areas where obviously the top surface has been drilled out or ground out, presumably by iron nodules such as the ones we find around the lake. Sandstone is not very soluble, so it's not so prone to forming these pockets and crevices as one typically finds in Limestone where both the action of the stone in a vortex and also water will quickly dissolve the hole. The structures present in the Lackagh sandstone formation are mainly mechanical. They would have been ground out like a millstone by something heavier, which to seems to point only to iron nodules which are typical in this formation or the formations above it.

This is an area needing much more study, particularly into its breeding birds earlier in the year, as well as its fascinating geology and flora. The photograph below is of an Iron Nodule picked up from the east Shore of Corry Island, in Lough Allen. They are common in the streams and lake shore. The text on the right is a Quotation from Geology of Sligo-Leitrim, Sheet 7, from the Geological Survey of Ireland. Anyone interested in Geology would be strongly advised to get their hands on a copy of that Map and Booklet. You may also access a Public Viewer and view the bedrock of the area HERE. But you will need to select the area and chose what geographical and geological elements you wish to view.



Brittle Bladder Fern (Cystopteris fragilis)


Iron Nodules

“Iron has been mined from Namurian rocks found on either side of Lough Allen. It occurs as Siderite (FeCO3) nodules, ranging in size from 15cm to 60cm, embedded in friable shales of the Dergvone, Gowlaun and Bencroy Shale Formations. The friability has lead to the soft shaley material being removed more readily and the resistant nodules being deposited in stream beds.

Mining was practised by scavenging these beds for the nodules... The nodules which average 40% metallic iron, were taken to local foundries for smelting. Production ceased in the last [19th] century.”

(Sheet 7, Sligo—Leitrim, Geologial Survey of Ireland)






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