The rocksconsist mainly of Namurian shale and sandstone beds, and the oldest rocks are under rocks. At the time of their formation

between 313 and 326 million years ago,a river dumped sand, silt and clay into an ancient oceanic basin.Over millions of years, the sediments

that had accumulated at the mouth of this ancient delta were deposited into sedimentary strata preserved in the now exposed rocks.

The area is considered a geologic laboratory that records delta deposits in deep water. The thickness of the individual strata ranged from

a few centimeters to several metres, each representing a specific depositional event in the history of the delta. In total, up to 200 m of

sedimentary rocks are exposed in the Cliffs of Moher. Trace fossils are abundant, including two main types (1) scolicia or worming trails,

which are interpreted as feeding trails left by as-yet-unknown invertebrates, and (2) burrow traces, which Bills once captured have rounded

features preserved in the form of yet unknown sea creatures.Wave marks are preserved in some stones.Today the rocks are subject to

erosion by wave action, which weakens the support base causing the rock to collapse under its own weight. This

process creates a variety of coastal landforms that are characterized by erosional shores such as sea caves, sea

stacks and sea stumps.Brannemore, a 67-metre-high seabed at the foot of the Cliffs of Moher below O'Brien Tower, was

once part of the cliffs, but coastal erosion gradually removed the layers ofrock that connected it to the mainland. A large sea arch can

also be seen at the head of the Haig under the Napoleonic Signal Tower and several smaller sea arches can be seen from sea level.