is strewn with
Turbidite The Clwydian Hills are formed from an upstanding block of
deep sea sediments formed during the
Silurian period as
debris slurries originating on the nearby continental shelf. The older
mudstones and
siltstones of the Nantglyn Flags Formation form parts of the west-facing scarp slope and the overlying Elwy Formation, which consists of mudstones and siltstones deposited in deep marine conditions with numerous
sandstone beds, forms most of the higher ground. Both formations are of
Ludlovian age. The range's rocks are intensely
faulted; the major Vale of Clwyd Fault is responsible for the impressive west-facing
scarp of the Clwydian Range. It downthrows the rocks to the west and separates the younger
Carboniferous and
Permo-Triassic rocks of the
Vale of Clwyd from those of the hills. Ice from the Welsh
ice-sheet moved eastwards over the Clwydian Hills during the
last ice age, impinging on the Irish Sea Ice to the east of the range. Numerous glacial
meltwater channels occur around the range whilst the valley of the
River Wheeler which cuts the range in two was a significant drainage channel. ==Geography==