A Guide to Cork City's Geological Heritage

A section behind the Inniscarra fuel station shows the variation of materials that these rivers left. The sediments can and should be admired from a distance, this location is not accessible and on private ground. But there is another location with similar Quaternary sediments situated idyllically along a riverbank. Along the easternmost boundaries of Ballincollig Regional Park is a beautiful river walk. The Lee meanders delightfully through the landscape here, with trees and convenient riverbanks along its sides. One of these riverbanks can be visited from the main path and provides an excellent vantage point to a beautiful outcrop of Quaternary sediments. While the outcrop is on the other side of the river, it can easily be admired from the accessible riverbank. The sediments were well-layered at the lower section of the outcrop where the rock materials seem to be smaller in size. This is likely due to lower energy levels in the flow of these meltwater rivers. When rivers flow powerfully, light sediments don’t deposit as easily and as such a lot what is eventually deposited are large pebbles, cobbles or boulders. However, in rivers with slower or less energetic flows finer sediments such as mud, silt and clays can settle more easily. As the river changes from calm to turbulent or vice versa, the grain sizes of the sediments reflect these changes.

Cork City has few exposed outcrops of Quaternary sediments. Glacial sediments are better exposed around coastal areas (most Irish geology is). This picture is from near Timoleague.

Ice sheets and glaciers are, like rivers, also forms of flow. During the last Ice Age, these ice sheets carried and transported boulders as large as houses several hundreds of kilometres away from their original position. As such, granite rocks from Galway appear down here in Cork. We call these boulders glacial erratics. By studying the sizes, shapes and sorting of different grains, pebbles and boulders in rocks and sediments, it allows us to get an idea of what took place back when these formations were created.