The immediate neighbourhood of Port Moresby strongly resembles a drowned coastline. The arches are very old sedimentary, short full of gypsum or infiltrated material and appear not to be very resistant to weathering. At the same time the great mass of the Astrolabe just behind P. Moresby is recent volcanic. Therefore perhaps the coastline sank (from loading?) at about the same time or just following the formation of the Astrolabe extrusions. At sea the fall is comparatively steep, the 100 fathom line being about 12 miles off shore. The islands clearly are drowned hill tops. If the age of Mt Faren and Yule and Astrolabe lands in Pleistocene and the topography of these regions and of the great limestone belt to the north is comparatively youthful then the greater part of the uplift of the geosyncline, wrapping the Torres area and sinking of the Moresby crant may well have taken place at one land and the same eon, namely during the Pleistocene.