Meath

Heritage Sites of Co. Meath

High Crosses, Kells

The monastic town of Kells, famous for The Book of Kells, also showcases a round tower and five ornately carved high crosses. The monastry at Kells was re-founded at the beginning of the ninth century by monks from St Colmcille’s of Iona, Scotland who fled from Vikings. Four of the crosses are located in the grounds of St Columcille’s Church. The famous Market Cross, originally located at the eastern gate of Kells (now Cross Street), presently stands outside the old Kells Courthouse (now the tourist information centre).

The Market Cross, once known as the Gate Cross on account of its original position at the entrance gate to the monastic settlement, stands 3.35 metres high and was carved in the late ninth or early tenth century. It consists of sandstone from Carrickleck, Co. Meath. This medium-grained, yellow Carboniferous sandstone has been used throughout centuries in Ireland for monumental and building purposes. The Carrickleck quarry produced sandstone that was frequently employed for dressed work in Drogheda, Co. Louth. Flagstones were also raised there; the cost of flags at the quarry during the mid nineteenth century was 10d. per foot chisseled and 8d. punched. This stone is still actively extracted today for disaggregated sand.

The crosses situated at St Columcille’s Church are also carved from sandstone, most probably from Carrickleck. The Cross of St Patrick and St Columba, also known as the South Cross, is the earliest of the high crosses in Kells, erected in the ninth century. It is carved from a single block of sandstone. Of the West Cross only the shaft remains, which is adorned with intricate carvings on four sides. The East Cross, or the unfinished cross, exhibits visible segments and provides an insight into how the high crosses were constructed. Rectangular panels are marked out on the cross ready for carving, however carving was never executed. Fragments of this cross were only reassembled and erected in the late nineteenth century, before which it lay in pieces. Only the base of the North Cross presently remains.

A detailed account of the history and carvings is available at http://www.megalithicireland.com/High%20Cross%20Kells.htm

Geology of Co. Meath

It is now well understood that Ireland is made up of two ‘halves’, which were originally separated by an ocean that geologists call Iapetus. The northwestern half was on the margins of a North American continent, whilst the southeastern half was on the margins of the European continent. Plate tectonic movement throughout the Ordovician period saw this Iapetus Ocean close and the two halves converge and eventually combine in Silurian times. Meath’s rocks tell part of this story and need to be understood in the wider context.

The oldest rocks in Meath are fine-grained sedimentary rocks of early Ordovician age that deposited in deep marine settings at the margins of the ancient Iapetus ocean. As Iapetus gradually closed during the Ordovician, by subduction of the ocean floor, volcanic rocks were erupted and built volcanic arcs (chains of islands) along the margins and within the ocean. Volcanic islands were centred on Grangegeeth and Bellewstown. By mid-Silurian times the ocean had narrowed. Silurian rocks are widespread, though generally not well exposed in Meath.

Then, the continents on opposite sides of the Iapetus Ocean were brought together, squeezing the oceanic sediments and volcanic arcs in between. The collision uplifted them to produce a range of mountains followed by prolonged erosion, which wore down the mountains so that the next stage of deposition followed a major gap in the rock succession.

The eroded mountains were covered by marine sedimentary deposits. As the sea advanced northwards, during the early Carboniferous, limestone sediments accumulated in slowly subsiding basins. Richly fossiliferous mounds of carbonate mud (“Waulsortian Limestones”) are common. Stretching of the Earth’s crust beneath Ireland during this period of limestone deposition allowed mineralised fluids to migrate faults in the rocks. These fluids sometimes altered the limestone into dolomite (limestone with magnesium in it). Other minerals, such as lead and zinc, also percolated up through these faults forming economic deposits within the limestone. These valuable ore deposits are currently being extracted in Tara Mines at Navan.

The youngest solid rocks in the county are found in a small area in the extreme north of the county and extend into the neighbouring counties of Cavan, Louth and Monaghan. A thickness of several hundred metres of dark grey mudstones and sandstones, sometimes with plant remains and thin coal seams, are of Carboniferous age and lie above the limestones. They are overlain by mostly red mudstones and sandstones of Permian and Triassic age, deposited between about 280 Ma and 230 Ma. Two thick beds of gypsum show that the climate at this time was harsh and arid. Still, younger rocks, around 60Ma, are the result of volcanic activity linked to the opening of the northern Atlantic Ocean. These are found as sheets, known as dykes and sills, of dark basalt lava that cut through the older rocks.

Till is a mixed glacial deposit of clay, sand and boulders, also called
boulder clay, left behind by ice sheets during the Ice Age. In Meath the till often takes the form of drumlins (the name is derived from the Irish ‘druim’ – small, round-backed hill or mound). Lakes often occupy the badly drained, inter-drumlin areas. As the ice sheet shrank towards the end of the glacial period, glacial debris was frequently deposited at the ice margin in the form of ridges called moraines. Many hummocky moraines occur south of Slieve na Calliagh. Large expanses of sands and gravels deposited by meltwater streams flowing from a glacier are common, for example in the Gormanstown and Summerhill areas and along the Boyne. An extensive system of eskers, which have been sorted and deposited as ridges beneath the ice sheet, occurs around Trim and Summerhill. Erosion by meltwater has cut some spectacular channels in the area, notably the Boyne Channel, with its tributary channels.

Geological map of Co. Meath

Map legend: Geological Map of Limerick (based on GSI 1:1,000,000 map 2003). Pink: Ordovician; Turquoise: Ordovician volcanic rocks; Grey green: Ordovician & Silurian sediments; Pale green: Silurian mudstones; Light blue: Lower Carboniferous limestone; Dark green: Upper Carboniferous shales; Brown: Permian and Triassic salts and sandstones.