Page:VCH Worcestershire 1.djvu/39

 GEOLOGY Martley. It yields corals, such as Halysites catenularia, and Favosites gothlandica ; crinoids ; the brachiopods, Strophomena depressa and iS". euglypha ; also the pteropod, Conularia. Among trilobites, Calymene blumenbachi, Phacops caudatus and P. doisoningice (the last named generally curled up) are characteristic forms. Referring to the interesting exposures of the strata at Dudley Castle and the Wren's Nest, Prof Lapworth remarks that ' the Silurian limestone rises up in steep dome-like forms. This limestone, which is that of the Wenlock [Dudley Limestone] of Siluria, is here composed of two calcareous bands — the higher about 28 feet in thickness, and the lower about 42 feet — separated from each other by an intermediate zone of about 90 feet of grey shales. The limestone has been worked for centuries as a flux for the ironstones of the [South Staffordshire] coal- field. The hills have been mined to a great depth, and all the best limestone rock extracted. The intervening and enveloping shales have been allowed to remain, and the present structure of the hills is that of a central dome surrounded by two enveloping shells separated from each other by two more or less empty spaces. Where the dip of the rock is higher, and these excavated parts are exposed, they form deep moat- like hollows bounded by walls of shale. Where the dip is low, and the overhanging rocks are supported by the vast pillars left by the workmen, these excavations form magnificent caverns of peculiar weirdness and beauty. In the heart of the hill at greater depths they form damp gloomy chasms of enormous extent, which can only be seen to perfec- tion when lit up by artificial light.' ^ At one time fine slabs of limestone with beautiful weathered-out examples of trilobites and crinoids, brachiopods and corals, were obtainable from the Wren's Nest. The Wenlock Limestone passes upwards into the Lower Ludlow Beds, which consist for the most part of grey shales. Here remains have been found of the oldest known fish, Scaphaspis ; also cephalopods, such as Orthoceras and Lituites ; starfishes, graptolites, etc. The Aymestry Limestone, which takes its name from a village north-west of Leominster, is a blue and grey concretionary limestone of somewhat inconstant character. It is characterized by such fossils as Pentamerus kntghti and P. galeatus^ Lingula, Cardiola, etc. The rock has been exposed at Hales End quarry, Malvern, and is represented also at Abberley. The Aymestry Limestone passes up into the Upper Ludlow Beds. These comprise shales with calcareous bands and thin-bedded sandstones. They yield brachiopods such as Chonetes lata and Discina ; also Serpuhtes, trilobites and other fossils. The strata are capped in places by a thin layer known as the Ludlow bone-bed, which contains coproUtes, minute scales and fin-rays, and other remains of fishes, including Onchus, Scaphas- pis, etc. ; also remains of the Crustacea Eurypterus, Pterygotus, etc. 9
 * Article 'Geology' in Handbook of Birmingham (Brit. Assoc), 1886, p. 229.