The Belemnite Marls of Charmouth, a Series in the Lias of the Dorset Coast

Abstract

Anyone standing on the beach between Charmouth and Lyme, and looking up at the bluffs and precipices of Black Ven, is struck by the contrast between the pale, blue-grey colour of the third, and highest, Lias precipice and the deeper shade of the underlying Black Marl. These pale marls, about 75 feet thick, soon pass off the eastern shoulder of Black Ven, but are readily picked up again as the eye follows the line of stratification eastwards, and across the valley, to Stonebarrow Cliff. There the pale marls make the second precipice, but soon dip to the beach to form most of the long, low cliff reaching from Westhay to the Ridge fault. These 75 feet of the pale marls are the Belemnite Beds of Day and of the Geological Survey. No adequate mention of them is made before 1863, when Day wrote his classic account of the Middle and Upper Lias of the Dorset Coast. although they are included in the ‘Upper Lias Marls’ of De la Beche's earlier account, and form the middle part of the eighth bed from the bottom of the section there described. In De la Beche's later account they occupy the middle of the lower part of his bed ‘a’: ‘Marls and slaty marls with several beds of indurated marl and earthy limestone in the lower part, micaceous in the higher—350 ft.’ In both accounts De la Beche particularly notes that belemnites are numerous, and other fossils occur in ‘marls on the shore, between