PROBLEM OF THE GREAT AUSTRALIAN ARTESIAN BASIN. 201 



and about Coonamble; the semi-saline magmatic waters 

 occupy the centre of the Basin, while the highly saline 

 residual types appear on the Gulf of Carpentaria, and along 

 the south-south-western margin between Bourke and Char- 

 lotte Waters. In the last-named region, analyses of the 

 waters both of the mound springs and of the marginal bores 

 exhibit high salinities — from 150 to 400 grains of salts per 

 gallon (I, App. Z; II, App. E). That the overlying Cre- 

 taceous marine beds are not contributing salt to the waters 

 of the springs in any marked degree in their passage to the 

 surface, is proved by the fact that, when bores are put 

 down in their vicinity (e.g., Coward, Warrangarrana, and 

 Hergott), the analyses agree closely, or the bore-water 

 has a somewhat higher salinity. 



The type of water in this quarter, instead of having a 

 high "primary alkalinity" is now characterised by both 

 high "primary salinity "and moderate "secondary salinity," 

 and in accordance with this new system of classification, 1 

 can be interpreted only as a trapped marine (connate) water 

 but slightly altered ; that of the Oodnadatta bore is a good 

 example. 



As already stated, of the dissolved solids, sodic chloride 

 exceeds sodic carbonate, while there is often a high pro- 

 portion of sodic sulphate and some magnesium salts as well. 

 In the deeper bores to the north-east, the waters are nearly 

 normal, as are also those from the mound springs between 

 Boulia and Cloncurry. Upon the hypothesis suggested the 

 high salinity of the water at Normanton can readily be 

 explained. 



It is most improbable that the leaching action of the 

 replacing waters could have been completely effective; thin 

 water horizons with weak circulation would naturally have 



1 C. Palmer, U. S. Geol. Surv., Bull. 479, 19 LI, and G. S. Sogers, Econ- 

 omic Geology, Vol. xn, p. 78, 19)7. 



