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Inch is a very popular locality for surfers, walkers, and holiday-makers, but for geologists and geomorphologists it is a special significant place.
Geologists would be found studying the solid nocks at the northern end of the beach and along the roadside overlooking the area. Here the Inch Conglomerate, an unusual and rare sedimentary rock, can be seen here. Conglomerates are coarse rocks containing rounded fragments of older rocks that have been cemented together. A close look at this rock (Figure 1) reveals cobbles of the pale-coloured metamorphic rocks gneiss and schist which have been dated to between 1.38 and 3.34 billion years old. These very ancient rocks were exposed at the Earth’s surface between 398 and 435 million years ago during the Devonian period and formed a mountainous area. The question facing geologists is: ‘where precisely was the source of the cobbles?’. Erosion has completely removed this past land area, but by examination of the arrangement of the rocks and the roundness of the cobbles one can be fairly confident that eroded material was transported by rovers some distance from the south towards the north where it was deposited as alluvial fans and turned into the rock we see today.
As well as the conglomerate, some sandy units contain distinctive burrows circular burrows called Beaconites and these were produced by lungfish or arthropods. These trace fossils preserve the activity of their maker but not the animal itself. The finest units of this group of rocks are reddish sandstones some of which have ripples on their surface.
Geomorphologists are interested in more recent aspects of the landscape and would be found studying the stretch of sand and the sand dune systems that project southwards for approximately 5 km into Castlemaine Harbour (Figure 2). Inch is one of the finest examples of a feature called a Spit. Together with those opposite at Cromane and Rosbehy, these spits hem in the course of the River Maine that flowed through the Castlemaine valley before it was flooded as sea levels rose after the Ice Age. Sand built up into a series of dune ridges and today the area supports a diverse flora. These dune systems are rather fragile and sand may get moved about in storms and new ridges of dune developed. A recent study has shown that the oldest dunes date back some 600 years.
Patrick Wyse Jackson is a frequent visitor to the Dingle Peninsula and teaches geology at Trinity College, Dublin.
