The Downtonian and Dittonian Strata of Great Britain and North-Western Europe

Abstract

I. Introduction The determination of a Siluro-Devonian boundary in Great Britain and north-western Europe has been dealt with by Barrels, Pruvost, and Dubois (1920), Stamp (1923), and Robertson (1928). My own investigation has been based in part on an application of the principles relating to deposition of sediments set out by Watts (1911), and more recently by Marr (1929). It has been shown (King, 1925) that the Down-Ionian and Dittonian strata of the West Midlands of England are mainly marls, belonging to one ldmud belt”, and laid down in epi-continental marine waters of moderate depth; and that they are a conformable sequence of beds transitional from the Upper Ludlow. The discovery, described later, of a shell fauna, abundant in individuals but sparse in genera and species, reaching nearly to the top of the Downtonian, is of some utility if considered in connexion with the Merostomata and fishes, and with the physiographical conditions under which these sediments with a “red fades” were laid down in north-western Europe. I have, therefore, investigated this region, in part personally and in part by making use of the work of others, so as to trace the “variable”, and “mud,” and “organic” belts (not oozes) laid down in the Siluro-Devonian period on this continental shelf, the continuation of a north-western land which at first encroached on the sea to the south-east, but in Devonian times receded again. The following divisions and stages are now adopted for the West Midlands, including the Black Mountains, where the Downtonian