The present-day arrangement of old ( ? ) Palaeozoic and Mesozoic metamorphic rocks in eastern New Guinea lends some support to the concept of tens:konal dilation in Upper Cretaceous to Lower Tertiary time, It appears that the metamorphic core of the Morobe Arc (Glaessner, 1950) could have been rifted from the eastern flank of Cape York Peninsula, and then been carried north-eastward by some unspecified sub-crustal. tangential force. In the early stages of the rift it is thought.that submarine basalts may have extruded up the .'tension .scar and spread across the floor of the opening rift. Thick clastic muddy sediments derived almost exclusively from the rifted block were then spread across the floor of the opening rift. Later ~ertiary lateral movements from east to west along the Markham-Ramu Fault appear to have bent the northern end of the Morobe Arc towards the.east,,causing the intense folding in the sediments of the Aure Trough.