20 E. CG. ANDREWS. 
gaps. Other shallow structural valleys occur within the 
plateaus and are arranged meridionally producing an undu--: 
latory appearance in some of the highland areas. 
The ring of sea troughs, such as the Tasman, Coral, and 
Arafura Seas, marks the first great outer division of the 
Australasian structures. Within these a few lines of low - 
islets are arranged subparallel to the Australian coast. 
These islet rings appear to be the structural counterparts. 
of the faulted and warped blocks of Central Australia. 
Other belts of islands with interinsular seas are repre- 
sented by New Zealand and its related groups. Two great 
structural lines, or zones, appear to run through the North 
Island, one passing through the northern extremity toward 
the islands lying to the north-west and the north-north- 
west, and one passing to the north-north-east towards the 
Kermadecs and Tonga. 
New Guinea, the Solomons, New Caledonia, and New 
Zealand, form the base of a great island knot which has its: 
north-eastern extremity in Samoa. The individual island 
loops of this knot appear to be separated from each other 
within the central portions but are continental and con- 
fluent, at the southern and western extremities. The knot 
itself would appear to arise as the result of the mutual 
interference of the Pacific and Tethyan controls mentioned 
above. This feature may be called the Great Southern 
Pacific Knot. 
The Gilbert, Cook, Society, and Paumotu, Gro form 
other belts of the same series. 
These island arcs or plateaus, measured from the indi- 
vidual and associated ocean trenches as datum bases, are 
higher than the eastern Australian plateaus. Moreover, 
the individual island belts are separated from others along 
the same cuspated zone by deep seas arranged along radial 
lines extended from South Western Australia. 
