The Lower Ludlow Formation and its Graftolite-Fauna

Abstract

I. Introduction. The Lower Ludlow Shales, which form the lowest section of the Ludlow division of the Silurian System, are most typically developed in the neighbourhood of the picturesque old town of Ludlow. It was in this district that they were first defined and described by Murchison. Lithologically, they are here essentially an argillaceous group of strata, the lower and upper limits of which are well marked by two distinct calcareous beds—the Wenlock Limestone below and the Aymestry Limestone above. Palæontologically, the Lower Ludlow Shales are rich in fossils: brachiopods, cephalopods, crustaeea, and graptolites. When the Lower Ludlow Beds are followed from the Ludlow district north-eastward along their line of strike as far as the valley of the Severn, south-westward as far as Aymestry, and eastward as far as the Malverns and Mayhfil, they are seen to retain their lithologieal characters unaltered, and the Wenlock and Aymestry Limestones are both well developed. But when these beds are traced from the typical area to the west and north-west, the limiting calcareous strata dwindle away and eventually disappear, until, finally, the Lower Ludlow Shales merge lithologically on the one hand into the Wenlock Shales below, and on the other into the Upper Ludlow Flags above. It is clearly impossible, therefore, in these westerly districts to separates on purely lithological grounds, the Lower Ludlow Beds as a distinct group from the formations which overlie and underlie them. The proofs that the Lower Ludlow Beds of Britain contain a Characteristic graptolite-fauna have been gradually