How Ancient Ice and Vanished Forests Shaped Our Irish Ancestors’ Lives

Céad Míle Fáilte, and welcome to your Letter from Ireland for this week. We’re motoring through February here in County Cork, and while today brings mild temperatures and that soft drizzle the Irish call “a grand soft day,” the landscape around me tells a much older story. Every hillside, every valley, every stretch of bogland we see today was sculpted by forces that ended just 12,000 years ago – mere moments in geological time. How’s the weather where you are reading from?

I’m warming my hands on a cup of Barry’s tea as I write, and I hope you’ll settle in with whatever you fancy as we explore something fundamental to understanding Irish history: how the land itself shaped everything – where our Irish ancestors could live, what they could grow, how they travelled, and ultimately, why so many of them had to leave.

When Ice Shaped Ireland

Last week, I received a thoughtful message from Thomas in Wisconsin that got me thinking about the deep foundations of Irish history:

“Hi Mike, I’ve been researching my family from County Mayo, and I keep seeing references to poor land, good land, bogland, drumlin farmland, and so on. I’m trying to understand why my ancestors lived where they did, and why they eventually had to emigrate. It seems like geography determined so much of their lives. Can you help me understand how Ireland’s landscape actually shaped Irish history and settlement? Thanks, Thomas.”

Thomas, your question touches on something genealogists often overlook – the physical landscape that determined whether our Irish ancestors thrived or struggled, stayed or sailed away. To understand Irish history, emigration, and even why your Mayo ancestors settled where they did, we need to go back to when Ireland was buried under ice up to a kilometre thick in some places.

The last Ice Age in these parts reached its peak around 27,000 to 21,000 years ago. Picture this: massive ice sheets covered virtually all of Ireland except for parts of the far south (probably where I am sitting right now!) These weren’t static frozen wastelands, but dynamic rivers of ice, grinding across the landscape, carving valleys, depositing sediments, and sculpting the Ireland we know today.

When the ice finally retreated around 13,000 to 11,000 years ago, it left behind a completely different landscape. In the midlands, it deposited gravels and clays in distinctive formations. There were eskers (ridges formed by glacial streams), drumlins (elongated hills shaped like upturned boats), and moraines (heaps of debris). Along the coasts, it carved dramatic U-shaped valleys like Killary Harbour in Mayo, Ireland’s only true fjord. In the mountains, it created sharp ridges and circular hollows called corries (from the Irish “coire,” meaning cauldron).

The Water Couldn’t Drain – And That Changed Everything

Here’s where the story gets crucial for understanding Irish settlement. All those eskers, drumlins, and moraines disrupted natural drainage across the Irish midlands. Water pooled in shallow lakes and hollows, unable to flow freely to the sea. In these waterlogged basins, dead plant material couldn’t fully decompose in the oxygen-poor conditions. Instead, it accumulated, layer upon layer, year after year, millennium after millennium.

This is how Ireland’s raised bogs formed – starting about 10,000 years ago in the midlands where annual rainfall was moderate. In the wetter west and in mountain areas where rainfall was heaviest, blanket bogs spread like a living carpet across hills and valleys. Some areas that farmed during the Neolithic period (around 5,000 years ago), are now buried under meters of bog. 

By the time human settlement intensified in Ireland, about 17% of the island’s surface was covered by peat bogs. This wasn’t empty wasteland, it was our Irish ancestors’ fuel source, but it was also land they couldn’t farm. The distribution of these bogs would fundamentally shape where people could live and prosper.

The Forest That Vanished

But there’s another part of this geological story that’s crucial to understanding Irish history, and one that transformed the landscape as dramatically as the ice itself. When Ireland’s first human inhabitants arrived about 9,000 years ago, they stepped into a land that was approximately 80% covered in dense forest.

Picture Ireland as it was then: vast oak and pine woodlands stretched across the lowlands, with hazel, birch, and elm filling in the landscape. The early Irish alphabet used tree names as letters – oak, ash, and hazel were sacred to the celts, believed to hold magical and medicinal properties. Many of our townland names, like Derry (from “Doire,” meaning oak grove), preserve the memory of forests that haven’t existed for centuries.

For the first few thousand years, hunter-gatherers had minimal impact on these woods. But when Neolithic farmers arrived around 6,000 years ago, everything changed. They began clearing land for agriculture – cutting and burning trees to expose rich woodland soils for cultivation and pasture. It was a pattern that would repeat, intensify, and accelerate for millennia.

As farming expanded through the Bronze Age and into the early Christian period, more forest fell. Around 800 AD, population growth led to thousands of ringforts springing up across Ireland, each one representing cleared land, grazing animals preventing seedling growth, and timber needed for construction. You may have seen the circular remains of some of these as you approach and airport for landing. 

Yet even with this gradual clearing, by 1600 Ireland still retained about 12% forest cover. What happened next was catastrophic. Under English colonial rule, Irish forests became both a strategic resource and a military target. There was even a proverb at the time: “The Irish will never be tamed while the leaves are on the trees.” The destruction of Irish woodlands was ordered to deprive insurgents of shelter, and to provide timber for England’s expanding navy. 

The 1606 Ulster Plantations accelerated the devastation. British “undertakers” received prime lands in Ulster, and their first act was typically to clear the forests – making land suitable for grazing while selling the valuable timber. Irish oak built ships that crossed oceans. It roofed Salisbury Cathedral, Canterbury, and Exeter. Beams from the Shillelagh woods of Wicklow went into St. Patrick’s Cathedral in Dublin. Irish timber became barrel staves for the wine and spirit trade with France and Spain, oak bark stripped for tanning leather.

By the mid 1600s, forest cover had collapsed to a mere 2%. The 19th century brought the final blow. Mobile sawmills travelled around Ireland cutting down the last remaining forests. By 1900, Ireland’s forest cover stood at approximately 1% – one of the lowest rates in all of Europe.

This deforestation had profound consequences beyond the loss of trees themselves. When forests disappeared, so did the shelter they provided, the timber for building, the fuel for cooking (why peat became so essential). Much wildlife vanished – wolves were hunted to extinction by 1786. The Irish word for wolf is “Mac Tíre”, literally “Son of the Countryside”, but the countryside could no longer support them.

The loss of forests also accelerated blanket bog formation in upland areas. Where trees once stabilised hillsides, their removal combined with climate change allowed peat to spread across landscapes that had once been farmed. 

The Good Land and the Poor Land

However, not all Irish soil was created equal by the retreating ice. Understanding this distinction is essential to understanding Irish history and why certain families ended up where they did.

The best land lay in the midlands and parts of the southeast, where carboniferous limestone formed the foundation. These limestone soils, covering almost a quarter of Ireland’s land area, were calcium-rich, well-drained, and naturally fertile. The grass that grew on limestone land was so nutritious it has become famous for producing Ireland’s finest horses – the limestone enriched the grass with minerals perfect for developing strong bones in young foals.

Counties Meath, Tipperary, and Galway had the largest expanses of this golden land. Farms here could support cattle and sheep year-round if managed properly. Tillage crops flourished. These were the areas that attracted the earliest substantial settlements and later, the attention of Norman conquerors and English planters.

Then there was the drumlin belt – stretching across counties Down, Monaghan, Cavan, Leitrim, and Louth. Drumlins (the word comes from the Irish “droimnín,” meaning “little ridge”) are those distinctive elongated hills that dot the landscape like an open box of eggs. The soil deposited here by glaciers was often fertile enough, but the terrain was challenging. Farms were smaller, more scattered. Yet these drumlins offered natural fortifications, which is why you’ll find so many ancient ringforts and crannógs (lake dwellings) in the drumlin belt.

And then there was the poor land. The mountainous west, the blanket bog regions, areas where thin soil covered bare rock – this was where survival was hardest. In Connemara’s granite landscapes, in Kerry’s mountain valleys, along Mayo’s windswept coast, families scraped by on tiny plots. They developed the “rundale” system – communal farming where the limited good land (the “infield”) was divided into scattered strips among families, while rougher “outfield” land was cultivated occasionally and commonage supported animals through seasonal grazing.

The Bog: Both a Blessing and a Burden

For centuries, Ireland’s bogs were both resource and obstacle. Documentary evidence shows peat has been used as fuel since at least the 8th century. After the destruction of Ireland’s native woodlands – particularly intensive in the 17th century under English colonisation – peat became the primary fuel for most Irish people.

Before the Famine, when Ireland’s population peaked at over 8 million, an estimated 6-7 million tonnes of peat were cut annually. Every rural family had turbary rights – the legal right to cut turf from local bogs. Interfering with these rights was one of the surest ways for a landlord to provoke disturbances.

The bogs also served as refuge and resistance. Their maze-like quality, with eskers providing the only reliable passes through extensive wetlands, sheltered people from invaders. Medieval clans knew every safe pathway through their local bogs. The great esker called the Eiscir Riata was an ancient highway through the midlands, marked by monastic settlements like Clonmacnoise that grew up along its route.

But bogs also represented lost agricultural potential. From 1716 onwards, the Irish Parliament passed Act after Act attempting to encourage bog drainage and reclamation. The English colonizers saw bogs as “wasteland” that should be converted to productive farmland. This often displaced people who depended on bog resources for survival.

Coasts, Islands, and the Sea Highway

While the interior presented challenges, Ireland’s extensive coastline – among the longest in Europe relative to land area – offered different opportunities. The same glacial processes that disrupted inland drainage created a dramatically indented coastline with countless natural harbors, sea loughs, and sheltered bays.

For thousands of years, the sea was Ireland’s highway. It was far easier to travel by boat along the coast than to trek across boglands and mountains. Viking settlers in the 9th and 10th centuries understood this instinctively – they established all of Ireland’s major towns (Dublin, Limerick, Cork, Waterford, Wexford) as coastal trading posts.

Ireland has hundreds of offshore islands – some historians count over 600, though only about 60 are inhabited today. The Aran Islands, the Blaskets, Tory Island, Achill, Cape Clear, Sherkin, Dursey – each developed its own distinctive culture shaped by maritime life. Island families fished in treacherous waters using currachs (lightweight boats), dragged seaweed from beaches to fertilize their thin soils, and built intricate patterns of stone walls from rocks cleared from their fields.

These islands weren’t isolated backwaters – they were connected to trading networks stretching to Spain and France. Archaeological excavations on Dursey Island in Cork found houses from the late medieval period dominated by Iberian pottery and roof tiles, evidence of extensive contact with Spanish fishing fleets. The Atlantic was a connector, not a barrier.

How Geology Shaped History and Emigration

Now we can understand how all of this shaped Irish history and why emigration became such a defining feature of Irish life, Thomas.

The fertile limestone lowlands supported larger, more prosperous populations. These areas were conquered and colonized first. The best land went to English and Anglo-Irish landlords. Native Irish were progressively pushed to marginal lands – mountains, bogs, rocky western coasts.

Population growth in the 18th and early 19th centuries hit these marginal areas hardest. Families subdivided their small holdings among children. The land could barely support one family, yet it was divided among three or four. People turned increasingly to the potato, which could produce more calories per acre than any other crop and could grow even in poor soil.

When the potato blight struck in 1845, it devastated these overcrowded marginal lands. The geology that made western counties like Mayo, Sligo, and Kerry so vulnerable – thin soil, excessive moisture, limited tillage land – turned a crop failure into a catastrophe. The drumlin belt of Ulster and Connacht, where farms were already small and subdivision had gone too far, suffered terribly.

But there was another factor that made the Famine catastrophic: the near-complete absence of forests. In earlier periods of hardship, Irish people could have relied on woodland resources – foraging for nuts and berries, hunting game, gathering firewood, finding shelter. By the 1840s, those options had vanished. The forests that might have provided supplementary food and fuel were long gone, replaced by exposed fields wholly dependent on a single crop.

Look at Mayo, Thomas – your ancestral county. Between 1841 and 1851, the population collapsed from 388,887 to 274,830. The blanket bogs couldn’t feed anyone. The thin coastal soils failed. The forests that might have offered some buffer had been cleared centuries before. There simply wasn’t enough good land to support the population that subdivision and potato dependency had created.

This is why emigration became not just common but necessary. The land itself – shaped by ice 12,000 years ago – determined who could stay and who had to leave. Emigrants from limestone lowlands of Meath or Tipperary might have had options. Emigrants from the bogs of Offaly, the mountains of Kerry, or the stony fields of Connemara often had none.

The geology explains the “ladder of emigration” too. Sons and daughters left first, usually women who found work as domestics in American cities. They sent money home – “remittances” that kept families afloat. This money often paid for siblings to follow. Between 1856 and 1921, women made up half of all Irish emigrants – extraordinarily high compared to other nationalities. They weren’t leaving opportunity behind; they were leaving land that couldn’t support them.

Reading the Landscape Your Irish Ancestors Knew

When you’re researching your Mayo ancestors, Thomas, look at the land itself. Was their townland in fertile valley bottom land or on exposed hillside? Near bog or on free-draining soil? Close to the coast or inland? These details tell you volumes about their lives.

If they farmed limestone lowland, they probably had options before emigrating – they may have left for opportunity rather than desperation. If they lived on blanket bog margins or mountain slopes, emigration may have been the only path to survival.

The 1901 and 1911 censuses ask about the quality of land – “1st class,” “2nd class,” “3rd class,” or “4th class” (bog or waste). This isn’t just administrative detail – it’s the story of your family’s daily struggle with geology.

Understanding how ice shaped Ireland’s landscape, how drainage patterns created bogs, how limestone formed good land while granite meant hardscrabble farming, how forests were systematically cleared – this explains patterns in Irish history that might otherwise seem random. It explains why certain areas emptied out during the Famine while others held population better. It explains why the west bled emigrants while the east urbanised. It explains why your Irish ancestors made the choices they did.

The Ireland we see today – its drumlins and eskers, its bogs and limestone plains, its dramatic coasts and scattered islands, its treeless fields and stone walls – all of this was shaped first by ice, then by water and vegetation, and finally by human hands removing the forests that once dominated the landscape. For 10,000 years these forces moulded the land. And then for a mere two or three centuries, that land shaped our Irish ancestors’ lives, determining who thrived and who emigrated, whose families expanded and whose were scattered across oceans.

Today, Ireland is slowly beginning to reclaim its forests. Reforestation efforts, native woodland schemes, and rewilding projects are attempting to restore what was lost. But in your ancestors’ time, Thomas, they lived in a largely treeless landscape carved by ancient ice, where the quality of soil and the distribution of bog determined everything. That’s the deep history beneath your genealogical research.

Thanks for such a thought-provoking question. I’d love to hear from our other readers – how do you think the landscape shape your Irish ancestors’ lives? What did they say about the land they farmed or left behind? Do leave your thoughts and comments below.

That’s it for this week.

Slán for now,

Mike.