QUATERNARY CLIMATE COMMirfEE. 24& 



Mountains," published in tlie Proceedings of the Linnean Society of 

 New South Wales of the following year (1907). Dr. Jensen returns 

 to the question in a paper entitled "The Nature and Origin of Gilgai 

 Country," (Journal and Proceedings of the Royal Society of New South 

 Wales, 1911). He says there (page 347), " Mammalian drift occurs 

 in places and gives evidence in favour of a moist if not a very wet 

 climate. The remarkable fauna of giant marsupials which existed 

 up to the end of the Tertiary period was decimated owing to the estab- 

 lishments of desert conditions. Drainage became disintegrated. Arid 

 erosion succeeded normal erosion. The present period can only be 

 described as subarid. There is sufficient rainfall to permit erosion to 

 take place and drainage systems have become re-integrated." Addi- 

 tional evidence of increased rainfall is afforded by the present creeks 

 cutting V-shaped valleys along the present watercourses through the 

 heavy thicknesses of tertiary and quaternary drift, especially along 

 their upper courses." 



The country in the neighbourhood of these mountains also afEords 

 evidence confirming the conclusion that before the present period was 

 one of more arid climate, and antecedent to this was another climate 

 distinctly humid in character and quite different from that now existing. 



An important investigation bearing on this question is that being 

 carried out by R. A. Cambage and E. C. Andrews, who are preparing 

 a joint paper on the " Late Tertiary and Recent History of the Eucalypts 

 of Australia." It is impossible, without prejudicing this paper, to deal 

 fully with the conclusions therein set out, but the following brief notes 

 indicate its general trend. 



It may be considered that the formation of the plateaus which 

 occupy the eastern margin of Australia date no further back than the 

 close of the Tertiary era, and that the profound gorges which dissect 

 the eastern portion of those plateaus are mainly Pleistocene in age. 

 A study of the flora of the coast strongly suggests that the climate has 

 there grown much more moist than in the period immediately prior. 

 Evidence is also to hand that the western slopes have also received 

 increased moisture, but this is based on doubtful evidence, such as the 

 isojated patches of desert plants found at the head of the Hunter 

 Valley, they being there out of their environment. Thus about one 

 acre of Yarran (Acacia homatophylla) occurs in the 8,000 square miles 

 of catchment, while one clump of about thirteen specimens of Brigalow 

 (Acacia harpophylla) and a few acres of Acacia Salicina and Hetero- 

 dendron olerfolium occur in the same locality. These trees grow freely 

 on the sub-arid inland plains. 



On the other hand, the centre and west of Eastern Australia 

 appear to be passi)!* through a slow desiccating process. Channels 

 once open are choked up and long lines of Eucalyptus populifolia and 

 aUied types alone indicate all but the main watercourses. It would 



