Heritage Sites of Co. Wicklow
Enniskerry is one of the most charming villages in Ireland and at its centre is a square clock tower, which acts as a focal and once utilitarian point. Erected in 1843 by Richard Wingfield, sixth Viscount Powerscourt, to commemorate the centenary of the creation (for the second time) of the peerage, aside from being a time keeper, it also provided water for man and beast via drinking fountains and bronze horse troughs. The latter are arranged on the outer perimeter walls of the platform and these are now used as planters, as are the bowls on the tower itself.
The tower was possibly designed by John Louch and is constructed of blocks of yellow-grey granite ashlar quarried from Glencree approximately 10 km west of the village. The pedimented tower has a clock face above an entrance doorway and two fountains emerge from the side faces, while the whole assembly sits centrally on a trilobate plinth of rough finished blocks of the same granite. The copper cupola on the top of the tower is a later addition of 1860 and was designed by the Dublin architect and onetime Lord Mayor of Dublin Sir George Moyers (1836–1913).
The Glencree Granite is one variety of several granite types that constitute the Leinster Granite. This was intruded during a major mountain-building event or orogeny at the end of the Silurian and beginning of the Devonian periods some 400 million years ago; it resulted due to the collision of two continents that came together as a former ocean closed. Granite was injected into the overlying crust in a series of plutons, each of which have slightly different mineralogical and textural characteristics. The size of crystals in granite is controlled by the rate of the cooling of the molten magma; smaller crystals indicate quick cooling and larger crystals slower cooling.
The Leinster Granite has long been used as building material in Dublin and the quarries on the western side of the Dublin and Wicklow Mountains at Golden Hill, Blessington, and Ballyknockan are perhaps better known than those on the eastern side of the mountains from which good quality stone was also procured. Here has been an equally long and proud tradition of granite quarrying from Ballybrew, Barnacullia, Glencree, Golden Ball, Stepaside, and Three Rock Mountain and examples of granite from all of these quarries can be found in Dublin.
Richard Wingfield, first Viscount Powerscourt, had stone drawn from Glencree on his estate for use in his country house at Powerscourt, built between 1731 and 1741. His second son, the third Viscount, also Richard, used granite from the estate for his Dublin town house on South William Street erected 1771–74.
The Enniskerry Clocktower should remind visitors and locals of the granite extraction industry that was active in the neighbourhood nearly three hundred years ago, and if not, a close examination of it will demonstrate the beauty of the Glencree Granite.
- Nicholas Ryan (1992) Sparkling Granite: the story of the granite working people of the Three Rock region of Co. Dublin. Stone Publishing, Dublin.
Geology of Co. Wicklow
The oldest rocks in Wicklow are those of the Cambrian period (550-490 million years ago [Ma]) that occur near Bray. These are a mixture of shales and greywackes that were deposited in deep water in an ocean called the Iapetus Ocean, which divided Ireland in two. Sandstones deposited in this ocean were later metamorphosed into quartzite and now make up the hard ridges of Bray Head and the distinctive Sugar Loaf mountains 9these are not volcanoes but owe their shape to the weathering characteristics of quartzite).
During the Ordovician period (490-450 Ma) Ireland was south of the equator and the Iapetus Ocean had begun to close. Sediments continued to be deposited off the land into this ocean and volcanic rocks were also produced in this tectonically active region. At the start of the Devonian (405 Ma) molten granite magma was injected into the overlying rocks, which were baked around the granite margins. At this time veins containing lead, zinc and silver formed in the granite. The granite was injected in several batches to form large masses called batholiths. As these cooled slowly below the surface they solidified into a coarsely crystalline rock. Eventually, 100 million years later, the overlying rocks had been eroded away so that by the Carboniferous period the granite was at the surface.
In the last million years Ireland was affected by the Ice Age. Glaciers flowed down mountain valleys forming ice sheets and eroded rocks and deepened valleys. When the ice finally melted, large lakes at Enniskerry and Blessington formed into which sands and gravels were dumped. These are now useful resources for building. Sometimes the melt water rushed through valleys like the Glen of the Downs and widened them.
Map legend: Geological Map of Limerick (based on GSI 1:1,000,000 map 2003). Pale yellow: Cambrian shales and greywackes; Dark yellow: Quartzite; Pink: Ordovician; Green: Silurian; Red: Granite; Turquoise: Ordovician volcanic rocks.