Excavations in Upper Teesdale, N. Yorks, exposed basement Carboniferous at its unconformable contact with underlying shales of probable Silurian age. The lowest basement beds are tough conglomerates cut by compression joints. The constituent pebbles are unsorted, locally derived, and mainly andesites and rhyolites, with vein quartz and shale pebbles. A dreikanter outline is common. The conglomerate is contrasted with others also between the Carboniferous and Lower Palaeozoic in England.