402 PROCEEDINGS OF SECTION E. 



little resemblance to that of the Liverpool Plains in which, as 

 described by Mr. T. K. Abbott in a paper read before the Royal 

 Society of New South Wales in 1880, an abundant and wide- 

 spread supply of water is obtained from wells. There can be no 

 doubt that the source of this supply is to be found on and near 

 the Dividing Range. 



When ve examine on a map the basin of the Darling and its 

 ti'ibutaries and follow the watersLed line from the source of the 

 Talbragar to the source of the Warrego, we find that there is a 

 great continuous amphitheatre of hills ranging generally from 

 2,000 to 5,000 feet in height, and that the rainfall on these hills 

 varies from twenty-two to thirty-five inches. Comparing a state- 

 ment of heights above sea level, which was most kindly supplied 

 to me by Mr. H. C. Stanley, Chief-Engineer for Railways, Queens- 

 land, with the information given by Mr. H. C. Russell in his 

 rainfall returns, I find that throughout the 23,650 square miles of 

 hills and tableland in the Queensland portion of the Darling basin, 

 the rainfall occasionally rises in several places to over forty inches 

 and seldom falls below twenty inches. There is some point here 

 in the question, "What becomes of the raiijfall?" While there 

 is no doubt that here also, evaporation and plknt life account for 

 a very large portion of it, it is beyond question that an important 

 share percolates underground. I have already pointed out in 

 reference to this question that tlie underground flow is subject 

 simply to the ordinary rules of hydraulics. Hence, with the same 

 class of material, the resistance to the flow will increase with 

 the distance from the source of supply. We find, therefore, that 

 near the foothills the supply in springs and wells is much greater 

 than at a distance. In fact the supply near the hills is in some 

 cases apparently inexhaustible ; while at a great distance down 

 the valley — for instance in the Bourke district — the springs tapped, 

 though most valuable, are mere driblets when compared to those 

 near the foot of the Dividing Range. Also, as the distance from 

 the source increases, and the flow becomes weaker, it is natural to 

 find that the quality of the water is frequently deteriorated from 

 its long contact with soil more or less impregnated with salts. 



A feature of this question which forms a popular stumbling 

 block is the unfailing nature of some springs and the apparent 

 uniformity of their supply. There is really nothing surprising in 

 this regularity when we come to consider its causes. Difierent 

 kinds of earths absorb in their interstices difterent proportions of 

 water ; the proportion in the case of sand being as much as one- 

 third of its bulk. In the instance of the Botany watershed 

 whose net area is 5,262 acres, the depth of sand varies fi'om 

 thirty-four feet to one hundred and nine feet. Taking the mean 

 of these depths — that is seventy-one and a-half feet — as the 

 average, and deducting five and a-half feet from this on account of 



