The fresh-water Triassic Esk Beds outcropping in the Esk Rift Valley between Harlin and Linville are about 10,000 feet thick, and consist chiefly of rapidly alternating quartz pebble conglomerates, dark green sandstones, and shales; the sandstones are mainly fresh-water greywackes. The Linville Tuff which occurs halfway through the sequence is a white lithic tuff of trachytic composition. Before being folded the sediments were intruded by the Balfour Trachytes-a suite of quartz_ and augite-trachytes; after the folding, the Nurinda porphyritic olivine microgabbro and the Brisbane Valley Porphyrites (now known to be dacites) were emplaced. The north-north-westerly trending structural pattern of the Esk Beds Is dominated by the Colinton Complex Anticline, an elongated structure with a maximum structural uplift of 10,000 feet. One of its major components, the Nurinda Anticline, is overfolded towards the west along most of its length. This is thought to be due to thrusting in the basement consequent on compression from the east, the forces being applied after rift formation and subsidence, and being followed by the period at tensional faulting and intrusion.