Black Rock Mountain is made of granites, igneous rocks, and slates and schists, metamorphic rocks, that formed more than 400 million years ago. During the last ice age, around 23,000 years ago, the ice across Wexford was at its thickest, reaching between 500-700 metres thick. As this ice moved, it carved and smoothed the landscape.
One of the most important features in this landscape is the blanket bog. Blanket bog occurs in mountainous areas which experience heavy rainfall. It started forming between 10,000-8,000 years ago. It consists of a type of soil known as peat, formed as rainfall dissolves minerals like iron and pulls them down to form a layer known as an ‘iron pan’ layer that stops water passing through. When the existing soil becomes increasingly waterlogged, any remaining plants start to rot. Over time, the build-up of rotting plants creates the dense black soil we call peat.
Tors, known locally as Brans, are granite rock formations that sit above the surrounding landscape. They were able to survive the action of the ice because of the strength of the rock. Other blocks of white and grey rock scattered across the landscape were broken off larger pieces by the action of ice. They were further weakened over a long period by different weather conditions and have been moved downslope by gravity to where they now sit.