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Mullaghmore ColLondonderry, Tyrone
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Summary Full report
Site Type: Inland exposure, Pit
Site Status:
District:
Grid Reference: X27384008, X26863986
Rocks
Rock Age: Quaternary
Rock Type: Gravel, Sand
Interest
Other interest: No data, Deglacial sediments, Glacio-fluvial sediment, kame terrace, meltwater channel, moraine ridge

Summary of site:

A compound col between Mullaghmore, Crockalougha and Glenedra has complex drainage; north westward into the Alnaheglish River, southwards via Barony Burn and the Altalacky River into the Douglas River at the head of the Moyola Valley and beyond Crockalough to the south and flowing along its south west flank, the Glenedra Water feeding north west into the Owenrigh River.

There are three groups of deposits formed during the retreat of the ice sheet from this area which are tentatively interpreted in this account. The first consists of three sites. At Carrickanullar at the head of the Glenedra Valley there are 4 ridges across the valley with a north west/south east orientation decreasing in length, depth and elevation towards the valley centre, the highest at the 380 m contour, and the lowest at 330 m. Exposure of the deposits is extremely limited but bedded cobbles and cross-bedded sands were seen, the latter indicating a supply and flow from the east. The second site has a set of deposits that form a group of flat-topped terraces about 1 km long, north west of the ridges. The upper surface is between the 320 and 330 m contours but only about 20 m above the valley floor. Small remnants of two other terraces at 300m and 295 m can also be seen along the river channel. The third site drains north west from Black Glen through a deep, narrow channel now feeding into the Altnaheglish River. A small tributary on the north side of the Altnaheglish Reservoir cuts through the col between Teevan Hill and Tamniarin Hill to the head of White Burn that drains directly onto the post-glacial Murnee delta. The second group contains two moraines. The first is a set of cross-valley mounds on a north west/south east trend with a second set along the line of the valley at Labbyheige Bridge. The second is at Kilcraigagh in the headwater of the Douglas River where a moraine belt crosses the valley towards Moydamlaght Forest where a pasty diamict and cobble conglomerate can be seen. The final phenomenon is the meltwater modification of the Carrickanullar ridges, the only site in the area to be affected. Poor exposure of the deposits makes the general events in the evolution of this landscape difficult to read but the simplest account visualises an ice lobe occupying the col that melted and wasted south into the Moyola valley. The Carrickanullar ridges are interpreted as moraines fronting the ice lobe in the col. These were later eroded by meltwater to create the terraces to the north. Similarly the hummocks at Labbyheige Bridge record a temporary standstill of the glacial front, with meltwater debris fed northwards through channels in the ice, before it then retired southwards. It stabilised again at the head of the Douglas valley, confining a temporary lake to the north. Sediments from the ice mass flowed into the lake and banked against the ice, leaving the moraine in its wake as it continued to waste to the south east into the upper reaches of the Moyola Basin. The glacial history of the col links several glacial retreat systems in the areas to the north, west and south. Strong bedrock landforms appear to have confined the ice in the col where two tongues formed, one in the Glenedra col itself, the other in Black Glen. A separate, smaller tongue appears to have occupied the Altibritain valley, eventually retreating south west into the Glenelly valley. Although there is a history of sand extraction, this is in general a rugged landscape marred only by the sand pit wastes. The only major threat could be further sand working.


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