Sandstone, a soft sedimentary stone, often appears in walls, buildings and elaborately carved Celtic high crosses. Unfortunately, it weathers poorly. Limestone appears mostly in monuments and in decorative and facing work. Often, highly polished limestone served as a less expensive alternative to marble. Basalt, an igneous stone, creates impressive natural structures, like Giant's Causeway on the Antrim coast of Northern Ireland.
Builders incorporate it into boundary walls and rough buildings.
Skilled builders use granite to create structures with precise dimensions. Single stone walls measure one stone deep. Their construction involves placing increasingly smaller stones on top of one another in pyramid fashion. Most commonly, single walls exist in Donegal, Down and the Aran Islands. The areas in which we traveled, however, had few examples.