The land included in the Moelyci project encompasses a tremendously interesting and varied geological section in a very small area. Climbing only 300m from the farm up to the hilltop, southwards, we traverse "up-section" that is up through geological time, spanning several episodes of continental break-up, basin formation, continental collision and mountain building. The section is dominated by a sequence of rocks of the Caledonian orogenic belt.
The oldest rocks we encounter are late Precambrian conglomerates, however they contain much older clasts, including jaspers, schists and gneisses that represent the oldest Southern British basement rocks. These clasts and the order in which they appear in the section provide evidence of the sequence of deposition and subsequent deformation, uplift and erosion during the late Precambrian Cadomian events (some 700-600 million years ago).

Overlying these are Lower Palaezoic and late precambrian sandstones, siltstones, shales and muds deposited in deep waters. The great pressures experienced by these deposits during the early Ordovician and late Silurian times, when the "proto-Atlantic" Iapetus ocean closed, was responsible for the generation from mudstone strata, the great seams of slate in the Penrhyn Quarry that dominates the view southwards from the top of Moelyci mountain.

The recent geology of the Ice Age is wonderfully represented in the landscape too, with moraine and esker gravel banks and "pingo" depressions formed by the melting of buried ice, also visible. These features are such fine examples of their types that students of geomorphology are regular visitors to an otherwise somewhat overlooked site of great geologic interest.