The Stratigraphy of the Valentian Rocks of Shropshire. The Longmynd-Shelve and Breidden Outcrops

Abstract

I. Introduction In Lower Valentian times South Shropshire was as yet uninvaded by the sea; but, by reason of the further subsidence of the south-eastern margin of the Silurian trough of deposition, the sea gained access to the region during Upper Valentian times. Doubtless as a result of the diversity of rock-types, the pre-Upper Valentian landmass exhibited a varied topography, which on partial submergence formed an irregular coast, similar probably to a rias coast. As first tentatively suggested by Callaway, South Shropshire may then have had the general appearance of an archipelago (La Touche, 1884, p. 14). The most important area of land in this complicated coastal region was that which is now known as the Longmynd and Shelve districts. On the northwest, the sea separated this area from the Breidden Hills, and on the south-east a narrow gulf intervened between the Caradoc Ridge and the Longmynd. On the south-east of the Caradoc Ridge was a more open and elongated expanse of water, which lapped against the main coastline situated still farther to the south-east. Thus the land was divided into three islands or peninsulas by gulf-like areas of sea, and the division is now reflected in the distribution of the three distinct outcrops of Valentian sediments fig. 1. Of these the most south-easterly has been selected as the type area and is known as the Main outcrop (Whittard, 1927). The next important development is the Longmynd- Shelve outcrop and the faulted outliers of Marshbrook