The South of the County is like a horseshoe stretching around Donegal Bay. The Bay washes the shore from Sliabh a’Liag to Bundoran, and the Croaghs or Bluestack mountains act as a granite boundary to the north, ending in Barnesmore (the "Great Gap") the gateway between north and south Donegal. The massive Sliabh a’Liag peninsula with the highest sea cliffs in Europe is the western boundary, while the Gweebarra river is the boundary with the Rosses and Northwest Donegal.

The land in the barony of Tirhugh - between Donegal Town and Ballyshannon - is good farming land, although the south west of the county contains extensive areas of rough pasture and upland bog as well as many lakes and inlets. The fertile area has been farmed since the early historic period, although archaeological evidence suggests that it was not settled in the Neolithic and Early Bronze Age era, perhaps because it was so extensively forested at the time.

The many small lakes are a feature of that part of south Donegal surrounding Lough Derg and adjoining Fermanagh. Lough Derg has been a centre of pilgrimage for centuries, and in medieval times was the only place in Ireland which most Europeans would have heard of. One can easily see why people believed that this barren area, with its thin blanket bog covering metasedimentary rocks, led to the gates of Purgatory. The original forests of the area have almost entirely vanished, but as late as the early 1600s there was significant afforestation in the South of the County. Dr. Eileen McCracken, in her study of the woodlands of Donegal, found that the area around Donegal Bay from Ballintra west to Killybegs was covered by trees, as was the area between Ardara, Glenties and Narin. The River Eske valley up to Lough Eske, well inland from the coast, and the area to the west of Lough Derg were also heavily forested.

Drumlins - tightly compacted and rounded mounds of boulder clay and sand and gravel, formed by glacial drift 10,000-12,000 years ago - are one of the distinctive features of the Donegal Town area. Druimlín means a 'little ridge or back’ and is the term applied to these hillocks usually between 60 and 100 metres high, although some are a little higher.

Drumlins are a feature of the geography of the southern fringes of Ulster, where the province meets both Connacht and Leinster. This drumlin belt has been a barrier to communication since prehistoric times and has acted as a cultural barrier for most of that time, being in effect the physical boundary between the provinces. The drumlins around Donegal Bay are thus part of a chain which extends across Ireland from here to Strangford Lough on the County Down coast. The swarms of drumlins around Donegal Town - along the eastern shore of Donegal Bay down to Rossnowlagh, and westwards as far as Bruckless - are the dominant feature of the landscape; they dictate the pattern of roads and fields, even to the present day, while the rivers, like the Eske, the Drummenny and the Eany Water have to negotiate their way around them to flow into the Bay.

Some 8,000 years ago, around 6,000 BC, Ireland’s climate began to enter a colder and damper period, resulting in much of the country being waterlogged, lack of drainage being a feature of glaciated areas. Low lying land and forests became marshes, but did not become lakes. Instead the partly decomposing trees and other plants formed peat bogs. There are extensive areas of blanket bog in the Gleann Cholm Cille (Glencolumbkille) area, much of them protected by law as repositories of a unique ecology, home to insect, animal and plant life which evolved there and which are not to be found in more fertile areas. The Pettigo and Lough Derg area also has extensive blanket bogs, vital to the inhabitants of these and other similar areas, as they continue to provide valuable fuel for domestic fires. While saving the turf is not as vital as it was until recently, with the availability of alternatives and changing working patterns even in remote areas, it remains an important feature, a ritual even, of the year’s work, involving the entire community. The time to cut the turf is just when the bog has begun to dry out but before it dries out too much, leaving the sod hardened. This is usually in late April or May, but like many other things in Donegal, it depends on the weather.

original Donegal library