The ancient Tomnafinnoge woodland lies among rolling hills, 90 metres above sea level. Like the rest of Ireland, everything that you can see in this woodland, like the soils, trees, and animals, were formed after the end of the last ice age, about 10,000 years ago. Underneath the ground we find till, a mixture of soil, gravel, and stones that were left behind as the glacier travelled. Most of the soils and peats in Ireland have developed on till, strongly influencing agriculture and human settlement. Tomnafinnoge sits on till mainly composed of sandstones and shale blocks, promoting the growth of deep fertile soils and lush woodlands.
The River Derry runs through here and beneath the water lies another glacial secret. This river was once a meltwater channel, formed by gigantic melting glaciers and the powerful flowing water they produced that carved and cut the riverbed. This channel carried both slabs of ice and icy waters during deglaciation, the period when the glaciers were melting and disappearing from the landscape.
Along the River Derry’s riverbanks, you will find small mounds of sand and gravel that were deposited by the glaciers.The mounds were formed as blocks of ice left behind by the disappearing glaciers melted away where they stood. Each block of ice would have carried a large amount of sand and gravel, and as the ice block melted the sand and gravel fell to the ground in these small mounds.