Post-auric age originally seems to have been in part an arid sea, and largely a dirty quartz sand. Such materials with the presence of feldspar leads to the conclusion that they are of post- murian deposition. This maybe so, but it should not be forgotten that then there was no land ardence to decompose the field spars. Thus the these deposits may afterwards be a delta or been a shallow sea deposit. It may well be that all of the Cambrian and Ordovician rocks of the Appalachia syn- syncline change towards the east to mud- stones. This will explain the absence in the Green Hills of limestones and dolomites, and the great thickness of sandstones here.