in Britain to yield Lower Cambrian fossils; the site at Comley Quarry is managed as a geological reserve in respect of its importance to the history of geological science. Ordovician Rocks of Ordovician age occur in a belt of country to the east of Church Stretton and again in a belt stretching south from Pontesbury through Stiperstones and westwards to the eastern side of the Vale of Montgomery. There is a further occurrence along the county boundary to the south and west of Oswestry. Silurian Worldwide the Silurian period is divided into four epochs; Llandovery, Wenlock, Ludlow and Pridoli, the second and third of which derive their name from Shropshire localities, reflecting the work of nineteenth century geologists in this area in understanding the rock sequences laid down during this period of geological time. The earliest Silurian rocks locally are the Pentamerus and Purple Shales formations, both being assigned to the Llandovery epoch. Their outcrop to the southeast of the Church Stretton Fault Zone extends from Wistanstow northeast to Buildwas. Overlying these to the southeast is the mudstone-dominated Coalbrookdale Formation which was traditionally known as the Wenlock Shale. It extends through the Sheinwoodian and Homerian ages which together constitute the Wenlock epoch. The Much Wenlock Limestone Formation (formerly simply the Wenlock Limestone) forms the long northwest-facing escarpment of Wenlock Edge. Immediately to its southeast is the discontinuous strike valley known as Hope Dale which is formed within the siltstones and mudstones of the Lower Ludlow Shales. Nowadays these Gorstian age strata are given 'group' status. A broken secondary scarp is formed by the overlying Aymestry Limestone Formation (formerly the Aymestry Group), also of Gorstian age. At the foot of its dip-slope are the outcrops of the Pridoli age Downton Castle Sandstone and Temeside Mudstone formations. At the base of the former is the Ludlow Bone Bed, representing the base of the Old Red Sandstone sequence of the Anglo-Welsh Basin. Further southeast again runs the parallel Corve Dale which is developed in the Raglan Mudstone Formation, also of Pridoli age. The southeastern edge of Corve Dale is provided by the outcrop of the overlying St Maughans Formation, the base of which is marked by the thick and regionally extensive calcrete known as the Bishop's Frome Limestone Formation which marks the transition from the Silurian to the Devonian. This unit was traditionally referred to as the Psammosteus Limestone. Small fault-defined inliers of