The Black Marl of Black Ven and Stonebarrow, in the Lias of the Dorset Coast

Abstract

The Black Marl series of the Dorset coast was so named by the officers of the Geological Survey to include the shales and limestones lying above the stone-beds of the Blue Lias and below the pale marls of the Belemnite Beds. I have already given a detailed account of the Shales-with-‘Beef’—the lowest part of the Black Marl series. But a detailed account of the sequence above the birchi bed is much needed; and, although our knowledge of the contained fossils and their order of occurrence is still incomplete, yet a particular description of these horizons as represented on the Dorset coast should help to unravel the sequence in the corresponding Lias of other areas, especially in view of the amount of work which is now being done on the Lias, and of the use already made of the Dorset sequence in such work. In this connexion much has been heard of non-sequences. It is hoped that this paper will show the importance of this principle in interpreting the Lias; yet to what error it may lead if rashly applied. I need hardly indicate how barren the detailed observations and descriptions of the paper would be without the accurate (even if approximate) determinations of the ammonites. Indeed, except from the view-point of lithology, detailed description of the beds is only necessary in order that the exact positions of the contained fossils may be recognized. The experience and the knowledge reuired to determine specimens as poorly preserved as most o those collected