Derryvree’s Cold-Stage Flora

Dateline

The label 31,139 BCE is a modern chronological convenience, not a year that anyone in Ireland could have named or recorded. At this depth of time there are no annals, rulers, settlements or events that can be assigned to a particular calendar year. In archaeological terms, the point lies roughly 33,100 years before AD 1950, within the Late Pleistocene and the later part of Marine Isotope Stage 3. The responsible scale is therefore not a single year but a broad, calibrated interval measured in centuries and millennia.

Ireland at this time was in the last Ice Age, but it should not be pictured as a uniformly frozen island. Climate repeatedly shifted between colder and relatively milder phases; ice margins advanced and retreated; and the surviving evidence is uneven. Much of what can be said comes from two very different archives: freshwater deposits sealed beneath later glacial sediment at Derryvree near Maguiresbridge, County Fermanagh, and animal-rich cave deposits at Castlepook, near Doneraile in north County Cork. Neither is a complete portrait of the island in 31,139 BCE. Together, they show that parts of Ireland could support cold-adapted life before the last major expansion of the Irish Ice Sheet.

Time Measured in Sediment

The clearest northern record is Derryvree, where a road cutting through a drumlin exposed organic silts and fine sands trapped between two thick layers of till, the stony debris left by glaciers. The sequence has a simple but important relative order: ice had occupied the area; a freshwater landscape later existed there; then renewed ice buried and preserved the deposit. A conventional radiocarbon determination on the organic layer, Birm-166, was published as about 30,500 radiocarbon years before present. Calibration gives a much wider calendar-age range, approximately 36,900–31,700 calibrated years before present.

That range embraces the broad period represented by 31,139 BCE, but it cannot date a particular season, generation or occurrence at Derryvree. It is evidence for an ice-free interval in north-central Ireland, not proof that every region was ice-free at the same moment. Nor does it establish a stable climate. The freshwater sediments formed in a cold, periglacial setting: ground subject to severe frost, seasonal thaw and sparse vegetation, rather than a modern woodland or pasture landscape.

The plant and animal remains in the Derryvree deposits point to open tundra-like conditions. Their significance lies less in a dramatic single find than in their combination. Organic material could accumulate in shallow freshwater or wet ground; plants and small organisms lived around it; and later glacial advance sealed the deposit below till. This is direct environmental evidence that an exposed, wet landscape existed in Fermanagh during part of MIS 3. It is not evidence for farms, villages or people there.

An Unsettled Ice-Age Island

At the island scale, the chronology of ice growth remains an active field of research. Models and landform studies agree that the great Last Glacial Maximum ice expansion occurred later, broadly from about 26,000 to 20,000 years ago, although individual sectors of the British–Irish Ice Sheet did not behave identically. The Derryvree sequence, alongside other pre-maximum deposits and cave records, matters because it preserves a world before that destructive phase. Subsequent ice cover scoured, reworked or buried much older ground surface across Ireland, helping to explain why evidence for this era is so rare.

South-west Irish caves supply a separate climate indicator. In Crag Cave, County Kerry, uranium-thorium dates show that stalagmites formed episodically during MIS 3. Stalagmite growth requires water to move through the cave and, in this shallow system, is associated with intervals when mean annual conditions were sufficiently mild for liquid water. That does not turn Kerry into a warm refuge, nor can a cave mineral date be translated into a precise weather report for all Ireland. It does, however, reinforce the wider conclusion that the Ice Age was climatically variable and that cold phases included intermittent environmental amelioration.

Sea level was lower than today because great quantities of water were stored in continental ice sheets, so coastlines and shallow seas differed profoundly from modern ones. Yet it would be unwarranted to draw a simple land bridge on a map or to assume that people and animals could always walk to Ireland. Glacial ice, rivers, marshes, exposed shelves and changing sea channels created shifting barriers and routes. The Irish evidence does not identify a route of arrival for any animal, still less for people.

The Castlepook Faunal Record

Castlepook Cave, also known as Mammoth Cave, is the most important Irish locality for the animal world of this broad period. Excavations begun by Richard J. Ussher in the early twentieth century recovered an extraordinary mixture of remains. The Pleistocene fauna includes woolly mammoth, reindeer, giant deer, brown bear, wolf, Arctic fox, mountain hare, lemmings and spotted hyaena. Taken together, these finds demonstrate that, during favourable phases before the Last Glacial Maximum, Ireland supported a much richer assemblage of large mammals and cold-adapted smaller animals than the island did in later history.

The list should not be mistaken for a census of creatures standing together in one Cork valley in one year. Cave deposits accumulate over long periods and can mix bones brought in by carnivores, animals that died after falling into openings, water movement and excavation disturbance. Re-dating with improved techniques has also shown that some earlier radiocarbon results for southern Irish cave bones were too young. The current evidence places important elements of the Castlepook fauna in MIS 3, while stressing that different specimens need not be contemporary.

Nevertheless, the ecology is telling. Reindeer and lemmings fit open, cold-country environments; Arctic foxes and mountain hares likewise indicate climates unlike present-day Ireland. Mammoth and giant deer required extensive feeding grounds, while wolves and spotted hyaenas show that predators and scavengers exploited the wider herbivore population. A hyaena den or carnivore activity may explain some bone accumulations. The cave therefore records animal movement, death and scavenging as much as it records the surrounding landscape.

The Reindeer Femur Question

One Castlepook bone has given this period exceptional historical interest: a reindeer femur reported as approximately 33,000 years old and bearing a deep linear mark interpreted by zooarchaeologist Ruth Carden as consistent with cutting or chopping by a sharp stone implement. If that interpretation is confirmed, it would be evidence that people handled a reindeer in Ireland during the Upper Palaeolithic, vastly earlier than the formerly accepted evidence for human activity on the island.

The conditional wording is essential. The specimen comes from an old collection, not from a modern, securely excavated occupation floor. No associated hearth, stone-tool assemblage, dwelling, burial, repeated butchery area or stratified campsite of this age has been published from Castlepook. A radiocarbon date measures the age of the bone’s surviving organic material; it does not separately date the incision, identify who made it, reveal where the animal died or show how long any people remained in Ireland. Taphonomic study must distinguish potential stone-tool marks from carnivore damage, breakage, trampling, weathering and old recovery damage.

The most that can responsibly be proposed is a possible, brief human episode during the broader period: perhaps a small mobile party encountered and processed a reindeer carcass. Even that is interpretation rather than a demonstrated settlement. It cannot establish a resident population, a migration route, a named group or direct ancestry for later inhabitants. The marked femur is important precisely because it is so rare, but rarity also limits what it can bear.

Society Beyond the Evidence

There is no basis for describing political affairs, diplomacy, warfare, leadership, law, religion, language, art or formal learning in Ireland at this point. There are no known Irish monuments, ritual deposits, graves, houses, tools in secure settlement context or artworks from which such institutions could be reconstructed. It would be misleading to project later Celtic, medieval or even Mesolithic ideas backwards into this far earlier landscape.

Nor can an Irish economy or trade network be documented. If people did briefly reach the island, comparison with Upper Palaeolithic communities elsewhere in north-west Europe suggests that mobility, hunting knowledge and flexible use of animal resources would have been vital. Reindeer elsewhere could provide meat, fat, hide, sinew, antler and bone. But Castlepook’s single disputed modification does not prove that these practices occurred in Ireland, and it certainly cannot establish exchange, seasonal scheduling or social organisation.

The defining historical development around 31,139 BCE was environmental rather than political: Ireland was a changing cold-stage landscape in which exposed freshwater basins, open vegetation and a diverse mammal fauna were possible before renewed glaciation transformed the island. Derryvree preserves the wetland evidence; Castlepook preserves an unusually rich faunal archive and a provocative but still limited human question. Both remind us that the earliest history of Ireland is not a sequence of dated deeds, but a painstaking reconstruction from sediments, bones, caves and ice.