Origin & Evolution

Origin: The pale grey to greyish-blue limestone layers or tiers that dominate the Burren were laid down at the end of the Lower Carboniferous (Visean) period, some 340 million years ago, in some cases to a thickness of 780 meters. This limestone is composed of the calcium-rich skeletal remains of marine organisms that populated the warm, shallow sea that lay over the region during that distant period. These were eventually compressed by their own weight and that of the sea above, and subsequently elevated to reveal the massive, fossil-rich beds that we see today.

Relatively insoluble shale bands separate these limestone beds, facilitating the formation of today's stepped landscape. These bands originate from ancient periodic fluvial outwashes of mud from adjacent land masses onto the sea bed. Later, in the Upper Carboniferous (Namurian) period, these fluvial outwashes of mud, sand, and clay became the dominant depositional form, and eventually (following compression) developed into thick (up to 330m) layers of shales, siltstones, and sandstones.

These darker, impermeable rocks once cloaked the entire Burren but were largely removed through glaciation, and now survive only intermittently in the west of the region around Lisdoonvarna (clearly visible at the Cliffs of Moher), and more consistently further south.

The Burren is quite stable geologically, as it is underlain by Tournaisian limestone, and further underpinned by Galway granite. Ancient earth movements have however affected the region, contributing to the formation of the distinctive web of joints - essentially vertical lines of weakness - that pervade the entire area, which when further weathered, develop into the characteristic clint-grike systems. These forces also resulted in the asymmetric north-east to south-west folding of the limestone layers in certain peripheral areas, such as the spectacular 'syncline' seen at Mullaghmore hill.

Evolution: The present day landscape of the Burren is a reflection of millennia of fluvial, glacial and solutional processes and, it would now appear, of anthropogenic (human) influence as well. The geological terminology most commonly used to describe the contemporary Burren landscape is 'glaciated karst', a reflection of the two most significant processes that sculpted it from the original, largely homogeneous, form.

Over the course of the last Ice Age, which began roughly one million years ago, much of the upper Namurian shales were stripped off the Burren, thereby exposing the limestone beneath to attack by erosive glacial waters, and subsequent scouring by the unremitting ice, removing any loose material. This tremendous erosive activity, acting along lines of weakness within and between the limestone layers, gradually etched out the distinctive terraces, pavements and other karst features visible in the Burren today.

The most recent glaciation (the 'Midlandian', 35-13,000 years ago) in the Burren proceeded from a north-east to a south-west direction, as attested by the orientation of the axes of glacial striations and drumlins. The main effects of this glaciation were further erosion and 'scouring', as well as the deposition of considerable amounts of calcareous drift, mainly spread along valleys, or alternatively in the form of drumlins, lateral moraines or fluvioglacial outwashes such as seen at Glencolumkille in the north-eastern Burren.

Relatively little sediment is thought to have been deposited in the Burren compared to elsewhere in Ireland, as the underlying karstic substrate and the proximity of the ocean provided escape routes for meltwater. As a result, only a light covering of distinctive rounded boulders (called 'glacial erratics) and sparse pockets of deposited sediment remained over large areas of the Burren, resulting in the very distinctive and unusual rocky landscape we see today.