68 AUSTRALIAN QUATERNARY CLIMATES AND MIGRATION 



level of the last glacial stage; from its outlet into the Araf'ura 

 Bight, there was probably a gorge some distance upstream cutting- 

 back into the mature erosion of the Pleistocene cycle, but the 

 soundings are not close enough to show tins. There was obviously 

 in ibis region some tectonic, movement, presumably subsidence, 

 but its nature and extent are not known. There is evidence of 

 another coastal plain at about 168 feet (Fig. 11) referred to here 

 as the Mid-Postglacial coastal plain, and a more recent one in 

 Torres Strait— the Torres coastal plain — at 54 feet (Fig. 11) ; but 

 its surface is generally masked by coral-growths. 



During the glacial period, the lower part of the basin of the 

 Flinders River was, for the most part, in the arid belt but in the 

 Mid-Postglacial period it was in the savannah (Fig. 13) with the 

 tropical rain-forest on the north about to encroach on its eastern 

 side. In the Mid-Postglacial period, the Flinders emptied into 

 a landlocked bay, an evolutionary stage of the Gulf, about 150 

 miles north of its present outlet. This bay was about 340 miles 

 long, subcircular at its southern extremity, but widening to a 

 width of over 200 miles at its northern end. Its waters covered 

 the basin of the drowned Flinders River of the glacial period, and 

 the bay had a narrow entrance from the Arafura Bight through 

 the drowned gorge. Immigrants, if they came by sea-travel, 

 passed up the channel and crossed the bay to its southernmost 

 extremity until they came to the outlet of the Flinders. 



In the glacial period much of the Northern Territory was in 

 the arid belt, as, too. was the Cape York Peninsula south of Point 

 Duyfhen. The northern part of the Peninsula was in the sav- 

 annah, also Tanimbar Islands, Aru Islands, and the coastal plain 

 for 50 miles north of the present shoreline of Melville Island. 

 The tropical rain-belt, extended north of a line approximately 

 coincident with the W.N. W. political interior boundary of Papua. 

 The line of maximum aridity — the middle of the arid belt — was a 

 few miles south of the present outlet of the Flinders River into 

 the Gulf of Carpentaria and trended W.N.W. to near the southern 

 extremity of Cambridge Gulf in northern Western Australia. The 

 arid belt itself reached about 350 miles further south to the 

 steppe-region and east to the rainfall-reliability belt which reached 

 as far north as the Atherton Plateau. The Flinders and 

 some of its tributaries carried off the rainfall of the latter, 

 and although the lower reaches of the trunk-stream flowed 

 through the arid belt, it was, nevertheless, a river of some volume. 

 When, however, it and its tributaries flowed over the Mid-Post- 

 glacial plain, it was not the full-flowing stream of the glacial 

 period, for its headwaters were not in the rainfall-reliability belt 



