Knocknashee Hill

Knocknashee hill is a fascinating place for both geology and archaeology. The archaeology comprises a hillfort, recognised as such only as recently as 1988, enclosing cairns and hutsites. Features to examine are listed below, and their locations marked on the more detailed of the maps to the left. Park at Dermot Scully's house, and enquire about access.

                                                                                                             
 

Archaeology:
1.The hillfort and sites within it.                                                 

• A Outer rampart
• B Inner rampart
• C Hut sites
• D Cairn and burial chamber
• E hollows (?habitation sites)
• F new walls
• G semicircular enclosures

2. Court "Abbey"

Geology (see text below for details)

• H rock outcrops
• J old quarries
• K "residual" deposit and peat
• F "missing" fossils
• D cairn and burial chamber materials

Geology and archaeology

Geology of Knocknashee

Knocknashee hill is similar in geology to Benbulben, consisting of a limestone top ( the Bricklieve Limestone) with shales (the Lisgorman Shale) underlying the lower slopes. The lower beds of the limestones can be seen in the quarries at J, where they are seen to be fine grained and dark, with interbeds of highly argillaceous limestone, nearly shale.

Beds higher in the sequence can be seen on the western side of the hill at H. The lowest exposures show irregularly bedded limestone with a diverse fauna of colonial and solitary corals, reminiscent of exposures at Ballyconnell on the Sligo coast, and as at that locality the fossils here are preserved in silica. At the time of deposition of the material that was to become limestone here, some 340 million years ago, Ireland was not far from the equator. The biodiversity suggests that the water was not deep, probably within the photic zone. Molluscs are notably absent from the fauna that we see in the cliffs. Their original shell chemistry differed from that of other fossils, and was not susceptible to replacement by silica.

At locality F where both involute and high-spired gastropods can be seen in the walls.

Rock outcrops below the main rampart on the west side of the hill. The most fossiliferous locality is out of sight to the left of the camera position.

a longitudinal cross-section through a solitary coral (Siphonophyllia) - by the coin, which is 3cm across; above it is a colonial coral, Lithodendron.

The rock layering, or bedding, in the hill area is tilted down a few degrees towards the southeast.

The hilltop is covered with areas of thin peat, which in places can be seen to cover the archaeological features. Near K is a small exposure of the peat, beneath which can be seen a thin layer of clay, weathered chert (pale colours compared with fresh chert which is bluish-black), and other non-limestone materials. This material is the residue of the weathering and solution of limestone and glacial till by slightly acid rainwater.

The hillfort and hutsites

The hillfort is bounded by two earthern or earth-and-stone ramparts. At A we see the outer rampart running from the camera point to the group of people. A rectangular hollow to its left, marked by a patch of rushes, marks an excavation of unknown purpose.

Outer rampart at A, and the Scullys' dog

The inner, and main, rampart occurs at or just within the break in slope which marks the rim of the interior plateau. On the east side of the hill it is camouflaged by a modern wall, but on the west, as at B, it may clearly be seen. Although now not very imposing, it was probably originally capped by a timber palisade.

the main rampart at B, looking southwest

Within the eastern part of the hillfort enclosure ( C ) are the remains of about 30 hutsites. These average 7-9m in internal diameter. Some of them display hollows on the outside from which the stone used to form the wall foundations has been removed. The roofs would have been supported by posts driven into the circular foundations. No excavations of the huts, nor other parts of the hillfort, have been undertaken.

a good specimen of a hut site, about 10m in diameter

Two large cairns are situated at the northern end of the hill. The western one has a fine megalithic burial chamber (on the capstone of which the Ordance Survey has erected a triangulation pillar...)

At the southern end of the hill at E, a short distance away from and inside the rampart, are a number of shallow and difficult-to-spot excavations. These may be a form of dwelling site (? - I wasn't paying attention at this stage of the visit... sorry). Just outside (to the south of) the rampart are a couple of walls of unknown purpose.

scooped out habitation site?

Further to the east, at F, are relatively modern wall structures. A look at the rampart here shows that material has been taken from it to build these walls.

On the east side of the hill, at G, two semicircular enclosures adjoin the main rampart. The larger of the two, to the north, is about 40m across.

Court "Abbey"

Court "Abbey" is a Franciscan friary, established by the O'Hara family, and dating from the 15th century. A square central tower stands at the junction of the east and west chapels. The stonework is in a dangerous condition. One hopes that restoration work is undertaken soon, and that this will avoid damaging the fragmentary remains of painted plasterwork.

A poorly preserved ringfort and a possible medieval field system is found just east and south of the friary.

Geology and archaeology

There are two interesting relationships between geology and archaeology here, both involving building materials:

1. A number of small disused quarries are to be found on the east face of the hill ( K ).
What could the stone have been used for? A survey of the adjacent countryside shows no stone walls, field boundaries being earthern banks. The material in the quarry shows two different types of rock: hard limestone, forming layers between 20 and 40cm thick, separated by slightly softer shaley limestone (limestone with an admixture of clay). These softer layers provide horizontal planes of weakness, allowing the extraction of limestone in blocks between 20cm and 40cm in thickness, suitable for building. A check of the nearby Friary shows that it's constructed of identical material, apart from a paler and more pure limestone which has been used for corners and window surrounds.

2. The building materials of the cairns, and of the burial chamber ( D ).
Although most of the cairn material is formed of limestone similar to that outcropping nearby, there are a few other rock types such as red sandstone and a limestone with pebbles of quartzite. In addition, the burial chamber at D has a floor and sides of grey sandstone, with a capstone of pebbly limestone. How did they get here? There are two obvious transport methods:

• by glacial action. The ice sheets of the last ice age picked up materials, and carried them considerable distances before depositing them again as glacial till (boulder clay), or as erratic boulders.

• by the cairn builders carrying them up the hill from somewhere.

How can we tell which method is the more likely? Clearly the first line of approach is to think geologically. Can we source the materials? The burial chamber capstone comes from the Dargan Limestone, whose outcrop is to the west and north of the hill. This would appear to rule out glacial transport, since the ice movement was from southeast to northwest (see Geology of Sligo-Leitrim, published 1996 by the Geological Survey of Ireland. But were I and my co-writers correct in saying that? Landscape features to the north of the hill seem to be contradictory. Oh dear..... More fieldwork is needed!

Michael Gibbons, and a distant Court "Abbey"