Derryvree’s Sedge-Moss Interval

Dateline

The label 31,602 BCE is a modern chronological convenience, not a date that can be matched to a recorded event in prehistoric Ireland. No calendar, settlement sequence or archaeological layer permits historians to distinguish this single year from those immediately before or after it. In radiocarbon practice, “present” is conventionally AD 1950, and samples of this antiquity require calibration because atmospheric radiocarbon levels have varied over time. The responsible frame is therefore a broad calibrated interval, not an annual narrative. Around this notional date, Ireland belonged to the later part of Marine Isotope Stage 3, an unstable phase of the last Ice Age preceding the fullest expansion of the British–Irish Ice Sheet.

A Date Within a Wider Interval

The most relevant Irish evidence comes from deposits rather than artefacts. At Derryvree, near Maguiresbridge in County Fermanagh, roadworks in 1969 cut through a drumlin and exposed freshwater silts and fine sands trapped between two separate sheets of glacial till. Organic material from these sediments produced a radiocarbon determination of about 30,500 radiocarbon years before present, with a substantial error range. Published calibrations place the deposit broadly between about 36,900 and 31,700 calendar years before present. Converted approximately into BCE terms, that span extends from roughly 34,950 to 29,750 BCE.

Thus 31,602 BCE falls within the wide chronological horizon illuminated by Derryvree, but it cannot be identified as the exact year in which the deposit formed. The sediments accumulated over time beside freshwater, while the organic remains within them may derive from several seasons or generations of vegetation. Their later burial beneath ice preserves a sequence of changing environments, not a dated episode in human history. This distinction is fundamental: the evidence supports a picture of cold-stage Ireland on a millennial scale, not a claim that a particular occurrence happened in this named year.

Freshwater Beneath the Ice

Derryvree is important because it records biologically active ground later overridden by glacier ice. Pollen, plant remains, mosses and insect evidence indicate an open, treeless landscape, with wet ground and freshwater pools among areas affected by severe frost. The original investigators described a vegetation unlike later Irish woodland: herbs, sedges and mosses were prominent, while dwarf shrubs and scattered low woody plants could exploit favourable niches. The term “muskeg”, used in discussion of the deposit, conveys the likely mixture of saturated, peaty vegetation and shallow water rather than a uniform bog of the modern Irish kind.

This was not an empty frozen waste. Even a cold, exposed landscape could contain productive margins around pools, seepages and watercourses. Sedges and other wetland plants supplied habitat for insects; insects in turn form part of food webs that could support birds and mammals. The local terrain would have varied. Low, waterlogged hollows, exposed mineral soils, river margins and sheltered slopes offered contrasting conditions within a relatively small area. Yet the Derryvree sequence should not be mistaken for a complete map of Ireland. It gives a sharply valuable local record from Fermanagh, not a survey of every coast, upland and interior plain.

Climate Before the Maximum Ice

At this time Ireland was in the last glacial period, but not yet at the Last Glacial Maximum. The main maximum of the British–Irish Ice Sheet occurred later, broadly between about 26,000 and 19,000 years ago, although the timing and extent of ice varied greatly between regions. Research on Irish landforms, marine sediments and ice-sheet modelling indicates a long, complex process of ice growth, advance and retreat. The broad Derryvree chronology is therefore especially useful: it demonstrates that ice-free freshwater environments existed in parts of north-central Ireland before a later advance laid down the upper till.

South-western Ireland supplies complementary evidence. Uranium-thorium dating of calcite formations in Crag Cave, County Kerry, shows that speleothems formed intermittently during Marine Isotope Stage 3. Because calcite deposition in such a shallow cave requires liquid water moving through the rock, these episodes point to intervals of relative climatic amelioration. They do not mean that Ireland was warm in any modern sense. Rather, the last Ice Age was punctuated by abrupt shifts, with conditions that could change markedly over centuries and millennia. A scene fixed permanently as either a wholly ice-covered island or a stable grassland would be misleading.

Animals and Open Country

Animal remains from Irish caves give a second, necessarily fragmentary perspective. Castlepook Cave near Doneraile in north County Cork has yielded one of the island’s richest Late Pleistocene faunal collections. Reassessment and improved radiocarbon pretreatment have shown that some remains once assigned younger dates are substantially older, belonging to Marine Isotope Stage 3. The wider assemblage includes evidence for animals associated at different times with open, cold-stage environments: reindeer, giant deer, woolly mammoth, brown bear, wolf, fox, hare, lemmings and spotted hyaena.

The list must be handled with care. A cave accumulation is not a census of a single landscape at a single moment. Caves can be dens, traps, drainage channels and places where bones are carried by carnivores, water or people. Many Castlepook materials were recovered during antiquarian excavations, before modern recording standards, and some deposits had been disturbed. Nor should every species be placed together in one imagined herd: redating indicates that the fauna represents more than one episode, while giant deer and spotted hyaena may have disappeared locally well before the later glacial maximum. What the cave securely demonstrates is that large mammals repeatedly reached Ireland during the Late Pleistocene and that the island formed part of a wider north-west European ecological world.

The Castlepook Human Question

A reindeer femur from Castlepook has made this broad period especially significant for Irish archaeology. County Cork heritage material identifies it as dating to about 31,000 BCE and records a deep mark interpreted by zooarchaeologist Ruth Carden as having been made by a sharp stone tool while a fresh carcass was processed. If that interpretation is upheld, the bone represents possible evidence for Upper Palaeolithic people handling reindeer in Ireland far earlier than the long-established evidence for terminal Pleistocene and Mesolithic occupation.

Its importance does not remove its limits. The radiocarbon result dates the animal’s death, not automatically the cutting action, the place where the animal was killed, or the duration of a human visit. Identifying a surface alteration as a tool mark is a separate taphonomic judgement, requiring comparison with carnivore damage, sediment abrasion, breakage and excavation disturbance. Most importantly, there is no securely associated stone-tool assemblage, hearth, dwelling floor, burial, human bone or repeated occupation surface from Ireland of this age. The marked femur may support the possibility of a brief hunter-gatherer incursion; it cannot demonstrate a permanent settlement, a continuous population or a named community.

No Kingdoms, No Recorded Society

There is no evidence from Ireland around this horizon for political institutions, rulers, diplomacy, warfare, tribal names, law or territorial boundaries. Nor is there Irish evidence for farming, herding, pottery, metalworking, monuments, writing, formal learning, long-distance trade in recognisable goods, or organised religious ceremony. It would be equally unsound to attach a later ethnic label, language or national identity to any possible visitors. “Irish” here describes the geographical subject of enquiry, not an ancient people known by that name.

If people did enter the island, the modest inference is that they were highly mobile hunter-gatherers able to use portable stone cutting tools and to exploit animal resources. Reindeer, if present in suitable numbers, could have supplied meat, hides, sinew, bone and antler. But even this describes a possibility suggested by a single object and wider European comparison, rather than a documented Irish economy. No evidence identifies whether visitors hunted an animal, scavenged it, processed it elsewhere before the bone entered the cave, or remained in the region beyond a short stay.

A Landscape of Evidence

The historical importance of this horizon lies in its restraint. Derryvree’s buried freshwater deposits show that parts of Ireland held open, wet and ecologically active terrain during a fluctuating Ice Age interval. Crag Cave registers episodes when groundwater moved and calcite grew. Castlepook demonstrates the presence, across different episodes, of a varied Pleistocene fauna and preserves a tantalising but still limited indication of human activity. Together they replace the old image of an unchanging, wholly ice-bound Ireland with one of regional variation, environmental change and fragile survival in the archaeological record.

For 31,602 BCE, then, the most responsible account is not of an event but of a changing country. Its waters, sedges, mosses, animals and advancing ice are better attested than its people. The silence concerning settlements and social life is not a gap to be filled with invention; it is itself the defining fact of Ireland at this depth of time.

Primary Sources

Tags: Castlepook Cave, County Cork, Derryvree, Ireland Year by Year, Late Pleistocene, Marine Isotope Stage 3