Old red sandstone is a sedimentary rock, meaning that layers of sediment are laid down and eventually solidify under their own weight. The layers that are formed are sometimes clearly seen as are some of the larger particles that form the sediment. Texture and composition of the rock can often depend on the conditions that prevailed at the time.
For example, here in Dunmore East, rock with differing sized peddles and small stones are solidified together. This may suggest a rough and tumble mixing of the original sediment. Such conditions may have been found in transient fast flowing water channels or an area that a flash flood might have spread across.
Old Red Sandstone at Dunmore East.
Also visible are fine grained red - orange sandstones. These might have formed as a result of sediment being laid down in a more gentle manner – at the bottom of a slowly moving river or deposited at a river delta. You can also imagine a scenario where a sandy desert plain is suddenly covered by a turbulent pebbly flash flood and the sand underneath becomes entombed and eventually solidifies.
The finer grained rock is known as sandstone, the coarser rock is a conglomerate. The characteristic red colour result from iron oxide (rust) coatings on the mineral grains in the rock. Iron oxide forms in relatively warm, oxidizing terrestrial conditions such as those that prevailed at the time. The rocks are rusty!!
What was this time period? In Geology terms this period was known as the Devonian period. It is generally accepted that the Devonian period lasted from approx 416 million years ago, to the beginning of the Carboniferous Period 360 million years ago. Around this time, this part of Ireland was situated near the equator and had a desert climate. The Devonian period has been also known well into the 20th century, as being "the age of fishes", referring to the great diversification of various fish groups in the period. While the development of fishes is of great importance from an anthropocentric point of view (inasmuch as they are our vertebrate relatives), the name is now avoided, as fishes where but one of several important groups to see extensive development in the Devonian. The name is frequently found in older (and a few newer) works.
All of the above aside, if you are not really interested in Geology, Dunmore East is a excellent place to visit. This cove is superbly sheltered and great for swimming. The village itself is picturesque and has a couple of nice pubs and restaurants. There are now plenty of caches around Waterford and the South East and this will make an excellent stop on a sunny day.
Safety: There is a two meter drop near ground zero so keep an eye out with the kids or in the dark, otherwise it is straight forward. This beach gets very busy in the summer, but the cache is findable with discretion. My advice is to park in the car park given at the waypoint below, it’s on the road to the golf course. The beach can be accessed from the village side also but parking will be a problem in high season. Also the part of the beach where the cache is may be cut off at higher tides. Don’t worry, from the car park approach the cache can be accessed at all tide levels. Enjoy.