THREE CRITICAL LOCALITIES ON THE JUNCTION OF THE BORROWDALE VOLCANIC ROCKS WITH THE SKIDDAW SLATES IN THE LAKE DISTRICT

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Abstract
Summary: Structural reinvestigation of the Manx Slates and Skiddaw Slates has shown that these rocks have been affected by three regionally recognizable episodes of folding and cleavage formation. A recent hypothesis proposed that in the Lake District the first two phases of deformation preceded the Borrowdale Volcanic rocks while the third affected the whole of the lower Palaeozoic sequence and was end-Silurian in age. In this paper the hypothesis of a lower Ordovician orogeny is tested against evidence from three well-exposed localities on the junction of the slates with the volcanic rocks. It is concluded that while there may locally be an unconformity of some magnitude at the base of the Borrowdale Volcanic Group, all three phases of deformation postdate the volcanic rocks and hence the hypothesis of a lower Ordovician orogeny in the Lake District is untenable.