Abstract

Triassic sediments are exposed on a 50-foot cliff on Sully island, off the coast of Glamorgan, southwest of Cardiff, Wales. The uppermost part consists of red and cream-colored marls and sandstones that exhibit structures varying from gentle to sharp isoclinal folds which die out downwards within 10 feet of the surface. The folds are not considered to be tectonic in origin as their direction bears no relation to the regional folding. They are interpreted as having formed under periglacial conditions, the gentle undulations resulting from differential squeezing caused by unequal freezing and the sharper folds resulting from the bursting through of ground water when the hydrostatic pressure increased from seasonal freezing. Comparison is made with similar superficial structures in the Keuper (Triassic) marl in Germany and in other places. The age cannot be precisely stated but may be Wuerm (Pleistocene).

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