BURNT KIMMERIDGIAN SHALE AT EARLY ROMAN SILCHESTER, SOUTH-EAST ENGLAND, AND THE ROMAN POOLE?PURBECK COMPLEX-AGGLOMERATED GEOMATERIALS INDUSTRY

Summary. A wide range of geomaterials were worked at industrial settlements scattered over an area of c.225 km2 in the Poole Harbour–Isle of Purbeck district of modern Dorset. These materials, more than one handled at some sites, included shale (‘coal’), burnt shales (yellow, red) and cementstones from the Kimmeridge Clay Formation (Upper Jurassic), Purbeck marble from the Purbeck Group (earliest Cretaceous), hard chalk from the Chalk Group (Upper Cretaceous), and potting clays and sands from the Bracklesham Group (Palaeogene), for South-east Dorset Black-burnished Pottery Category 1. There was also a salt industry, which could have used pottery for packaging. The industrial products are conterminously distributed in southern and central Britain and, in the case of pottery and shale items, reached as far as the northern frontiers. Raw material of red burnt shale was exported to Silchester (Calleva Atrebatum), where it was made into mosaic tesserae. Of proven Kimmeridgian age on the evidence of fossils, the mudstone used to make it had been collected and quarried on the coast of the Isle of Purbeck before being burnt. The decline in the demand for stone products, excepting shale, in the second century AD saw an expansion of the potting industry, which persisted into the fifth century. The term complex-agglomerative is introduced to describe this diverse and dispersed enterprise at this highest hierarchical level, examples of which occur elsewhere in the Roman world.