398 PROCEEDINGS OP SECTION E. 



taken place in the eccentricity of the earth's orbit, and by the 

 deflection of ocean currents ; the second of these causes being in 

 a very large degree a consequence of the first. That ocean 

 currents have an important influence on climate has long been 

 known ; but this influence was placed in startling relief when 

 Dr. Croll showed that " but for the gulf stream and other cur- 

 rents, London would have a mean annual temperature forty 

 degrees lower than at present." 



To Mr. C. S. Wilkinson, Government Geologist of New South 

 "Wales, is due the credit of first applying to the case of Aus- 

 tralia, the principles which have been accepted in explanation of 

 the changes of climate in the Northern Hemisphere. The results 

 of his investigations which were given in his Address as President 

 of the Linnean Society of New South Wales in January, 1885, 

 are most interesting and instructive in their bearing on the 

 formation of the great alluvial deposits of this colony, and on the 

 present stage of development of our rivers. It is unnecessary 

 here to follow Mr. Wilkinson in his description of the causes of 

 the high rate of rainfall during a past epoch in the western plains 

 of New South Wales, whei*e the I'ainfall is now light and uncer- 

 tain. That the conditions of rainfall and of vegetation, particu- 

 larly in the western parts of this colony were entirely different to 

 those now existing is proved by one circumstance alone — namely, 

 the existence there of gigantic animals, such as the Diprotodon, 

 which could not live under present climatic conditions. Mr. 

 Wilkinson calls special attention to the significant fact that the 

 largest find of fossil remains of large extinct animals in the 

 western part of New South Wales — namely, that at Cuddie 

 Springs, fifteen miles south of the Darling, near Brewarrina, was 

 in a boggy spring on the open plains and about ten miles distant 

 from the nearest watercourre. It has been said that we live in a 

 zoologically impoverished age in which the largest and most 

 striking forms of animal life have dwindled, or become extinct. 

 That this remark applies accurately to New South Wales, is placed 

 in a remarkably clear light in Mr. Wilkinson's Address to which 

 I have referred. Whilst there are questions which only the 

 geologist can investigate, their practical bearing on the develop- 

 ment of our rivers must not be lost sight of. The researches of 

 the historian are not more necessary to the statesman, than are 

 those of the geologist to the engineer who deals with rivers and 

 water supply. 



As I have already pointed out, the position of the source of a 

 river is constantly varying. It is an evident consequence of this 

 that the effective catchment area is also indefinite. In steep and 

 impervious ground a very slight fall of rain is sufficient to cause 

 a flow of surface water ; but as the slope of the catchment area 

 diminishes, and the ground becomes more permeable or more 



