BY ROBERT L. JACK, F.G.S., F.R.G.S. 61 



ments of the amount of water absorbed by these Queensland 

 rivers, I quoted, as a parallel instance, Mr. H. C. Russell's 

 calculations relating to the Darling. " The mean annual rain- 

 fall on the Darling River catchment for the past ten years has- 

 been 22.14 inches, and of this only 1^ per cent, or 0.33 inches 

 of rain passes Bourke in the river. If 25 per cent, of it, which 

 is equal to 5.53 inches of rain, passed away in this river, as it 

 does in the Murray, there would be seventeen times as much 

 water passing Bourke as now actually does pass. . . . And 

 we ought, therefore, to have an underground water supply at 

 least equal to sixteen times as much water as passes Bourke 

 now. . . . That we do not find it in the Darling is to my 

 mind proof that it passes away to underground drainage." To 

 make Mr. Russell's argument clearer I ought to have had quoted 

 this further passage : — " The Darlmg carries away only li per 

 cent, of the rainfall, while the Murray, a river existing under 

 similar conditions of climate, wind, rain, and evaporation 

 carries away 25 per cent, of the rainfall. The only difference I 

 can see which seems to offer any clue to this great disparity 

 . . is in the extremely porous character of much of the 

 Darling basin." 



Mr. Thomson, in discussing Mr. Cox's paper, pointed out 

 that recent measurements* show that not Ih but 6 per cent, of the- 

 annual rainfall on the total effective catchment area of the Darling 

 above Bourke (which is 20 inches instead of 22.14 inchest) passes 

 Bourke in the course of the year. Assuming the accuracy of those 

 figures, I do not see that Mr. Russell's argument is impaired. The 

 rainfall is distributed in three ways : One portion sinks into the 

 earth, not to return except through springs or submarine leakage ;: 

 a second portion is evaporated ; and a third is carried off' by the 

 watercourses which drain the surface. Whatever figure we 

 assume or ascertain for the amount drained by the watercourses, 

 the remainder of the rainfall must be divided between evapora- 

 tion and absorption. Even if G per cent, of the rainfall is carried 

 oft" as drainage by the Darling valley, the remaining 94 per cent, 

 will surely leave enough both for absorption and evaporation. 



* Annual Report of the Chief Engineer for Water Conservation, New South 

 Wales, for 1891. 



I Mr. Russell informs me that in 1891 the rainfall over the Darling .area was- 

 27.27 inches. 



