PROBLEMS OF THE ARTESIAN WATER SUPPLY OF AUSTRALIA. 131 



discharged 31 times more rainfall than a similar area of Darling 

 watershed. In the above the abnormal drought year 1902 is 

 included, and perhaps it might be regarded as unfair to include 

 such a year in comparative records of run-off. If 1902 be excluded 

 for the period under review, we find that the proportion of 

 rainfall discharged from the Murray catchment is 12 times greater 

 than that of the Darling. The volume discharged by each river 

 must not be confused with the percentage of run-off, as the 

 Murray at Wentworth does not discharge anything like 12 times 

 the volume sent down the Darling channel. This, of course, is 

 obvious, as the Murray watershed is so much smaller than the 

 Darling. 



"The information on which the above calculations are based, is 

 as complete and reliable as it is possible to attain with the 

 available data of river discharges and rainfall observation and may 

 be accepted as within the reasonable limits of accuracy." 



It is evident from Mr. McKay's very interesting results, 

 that, although the late Mr. Russell's figures were based 

 upon very imperfect data, they were not, after all, for pur- 

 poses of comparison, so very far from the truth. 



It may therefore be regarded as a fact that the ratio of 

 run-off to rainfall in the case of the Murray is very much 

 higher than it is in the case of the Darliug, and this is 

 undoubtedly due to marked differences in the geology of 

 the two catchment areas. The tributaries of the Murray 

 (above Wentworth) all flow over granitic rocks, or dense 

 palaeozoic sediments; on the other hand, all the tributaries 

 of the Darling, in their upper reaches, cross the porous 

 intake beds of the artesian basin, and thus a large propor- 

 tion of the rainfall finds its way underground, and feeds 

 the flowing wells. These tributaries of the Darling are 

 the Bogan, Macquarie, Oastlereagh, Namoi, Gwydir, 

 Mclntyre, Dumaresq, Culgoa, and Warrego. 



Evaporation.— Professor Gregory discusses at consider- 

 able length the question of evaporation, and endeavours 



