Type Group Thickness up to 1800 m Named for Snowdon | Overlies Cwm Eigiau Formation Primary ash flow tuffs | |
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Sub-units Upper Crafnant Volcanic Formation, Middle Crafnant Volcanic Formation, Lower Crafnant Volcanic Formation, Tal y Fan Volcanic Formation, Bedded Pyroclastic Formation, Lower Rhyolitic Tuff Formation Underlies Cadnant Shales Formation etc | ||
The Snowdon Volcanic Group is an Ordovician lithostratigraphic group (a sequence of rock strata) in Snowdonia, north-west Wales. The name is derived from Snowdon, the highest peak in Wales where it outcrops. This assemblage of rocks has also been referred to as the Snowdon Volcanic Series.
Contents
Outcrops
The rocks occur across the Snowdon massif and to its south, southeast and west, around the eastern flanks of the Carneddau and within the Idwal syncline.
Lithology and stratigraphy
The Group consists of up to 1800 m thickness of ash flow tuffs with sandstones, mudstones and siltstones and important basalt, hyaloclastites and breccias erupted or sedimented during the Caradocian Epoch of the Ordovician Period. The Group includes (in descending order, i.e. oldest last):
The Tal y Fan Volcanic Formation occurs towards the northeast and the Bedded Pyroclastic Formation and Lower Rhyolitic Tuff Formation occur to the southwest.