317 



It will be seen that there is on the map what may be termed a N.eutra,! 

 Line ; that is, a line where the equivalent quantity of the sulphuric is equal to 

 that of the carbonic acid radicle. This line approximately indicates the meeting 

 of the eastern and western waters. The gradual relative decrease in SO4 from 

 west to east is probably accounted for by the interchange of alkali sulphates 

 and carbonate of lime in the aquifer giving soluble alkaline carbonates and 

 gypsum which is held in the porous sand beds. For example, the Arckaringa 

 water contains less gypsum as it is followed eastward, and it is very probable 

 that if this water travelled as far as the eastern water has done it would be 

 wholly carbonate and not sulphate. The Neutral Line lies east of Anacoora 

 and Allinga Bores, west of Dalhousie Springs, east of Horseshoe and Oodnadatta 

 Bores, and thence east of the Denison Range, to between Strangways and 

 Coward Bores. The line is a fluctuating one, its position depending on the relative 

 draught on and intake of the eastern or western water. As plotted, out of the total 

 area of the South Australian portion of the Artesian Basin, of 106,740 square 

 miles, 22,200 square miles, or 264 per cent., is fed by the western water. 



On the plans are marked, as small crosses, all the groups of mound springs 

 that are named on the South Australian 16-mile map, and the relation of the iso- 

 potential lines to them is very marked. A map of the Great Basin, prepared by L. 

 K. Ward and published in the "Annual Report of the Government Geologist for 

 1921," shows that in the Eastern States there is a similar and marked fall of 

 potential near the mound springs, and leaves no room for doubt as to the springs 

 having been the normal main escape vents for the water before boring was 

 started. Plans Nos. 2 and 3 show two sets of data : the total salts and the chlorine, 

 in grains per gallon. 



These isopleths of salinity and the iso-chlors agree on the whole very closely 

 and bring out several features that were not apparent on the first plan. They 

 show the good quality of the eastern water, and that it gradually increases in 

 mineral content as it travels westward. 



The exceedingly variable character of the western intake water is made 

 clear. The Goyder and Finke and Alberga feeders draining from high land, 

 and so, being large, give good water. As it travels underground towards its 

 natural outlets (the Mound Springs west of the Denison Ranges) it becomes 

 worse in quality, partly no doubt by the solution of material in its path and 

 partly by admixture of the lower-quality waters from the upper Arckaringa and 

 southerly intakes, which are seeking the same outlet. The Arckaringa feeder 

 is less efficient and so the water is of poorer quality. Thence to the Stuart 

 Range Bores the quality is bad, as is only to be expected from the absence of 

 run off and the scanty rainfall. These maps also show very clearly that there is 

 an intake west of Strangways, where Warriner and North Creeks supply poor- 

 quality water of the sulphate type. This tongue of bad water thrust into the 

 better-quality eastern water gradually becomes diluted. 



The most significant is the great tongue of good-quality water that makes 

 its way past Jewellry Creek Bore to the Bopeechee-Coward groups of springs. 

 A less-defined one leads towards Petermorra and Paralana Springs, and there 

 is also a tongue of good water extending from the east towards the springs 

 between Lake Eyre and Denison Ranges. 



The total salinity isopleths and isochlors have very great significance, as 

 they indicate that there is a very pronounced differential movement in the 

 underground water, and that this movement is towards the natural outlets. 

 Furthermore, it argues the antiquity of these outlets, as the water flowing directly 

 from intake to outlet has had time to flush out zones through the older and 

 more stagnant and consequently more highly mineralized water, and to refill 

 them with fresher water. 



Still another deduction that may reasonably be drawn is the very considerable 



