The succession of the Lower Old Red Sandstone (Siluro-Devonian) along the Ross-Tewkesbury Spur Motorway (M.50), Hereford and Worcester

The motorway cuts approximately 1900 m of strata, of which about 56 per cent are continuously exposed in numerous long sections, a new standard being afforded for the Lower Old Red Sandstone in the southern Welsh Borders. The succession recognized is: LOWER OLD RED SANDSTONE Brownstones (L. Dev.) at least 795 m St. Maughan's Group (L. Dev.) 630 m Raglan Marl Group (Siluro-Dev.) 385 m Clifford's Mesne Sandstone (Sil.) at least 9 m LUDLOW SERIES (Silurian) at least 5 m The uppermost Ludlow Series and the Clifford's Mesne Sandstone are exposed in the core of the May Hill-Woolhope upfold. They are overlain in the complimentary syncline to the west by the Raglan Marl Group, St. Maughan's Group and Brownstones, in ascending order. Above the Clifford's Mesne Sandstone, there is a progressive upward increase in the number and thickness of sandstone relative to mudstone beds. Pedogenic limestones are largely concentrated in two short stratigraphic intervals. The lowest, mainly in the uppermost Raglan Marl Group but reaching into the St. Maughan's Group, includes the “Psammosteus” Limestone recognised elsewhere in the area. The second concentration occurs in the uppermost St. Maughan's Group. Vertebrates in the Raglan Marl Group and the St. Maughan's Group allow the Downtonian and Dittonian “stages” to be recognized.