PROBLEM OF THE GREAT AUSTRALIAN ARTESIAN BASIN. 165 



that any of the oxygen originally dissolved could have 

 escaped being used up long ere the waters reached this 

 point. 



The sodic carbonate over the Basin generally ranges 

 between 20 and 60 grains per gallon, and with the excep- 

 tion of Bromanga No. 2 (121 grs.) and Normanton (160 grs.) 

 the high values are all along its intake edge, e.g., Barcal- 

 dine and Blackall (64-70), Dalby (67), Baroma (67), 

 Tunderbrine No. 1 (125), and the bed-rock bore at 

 Narrabri (671). 



Suggestive indeed is the occurrence of waters of this 

 class, both along the outer edge of the Basin — the Ballimore 

 bore, east of Dubbo (196 alkaline bicarbonates) the Helidon 

 Spa belowToowoomba (212 sodic carbonate, 3 sodic chloride) 

 — or further afield, as at Maria Creek on the Central Rail- 

 way (576 grains) with pulsations of carbon dioxide, and 

 several hot springs north-east of Hughenden between 

 ■Georgetown and Chillagoe, to be cited later. 



Obviously the carbonates could only have been formed 

 by the prolonged action upon soda-bearing minerals of 

 carbon dioxide — of which the artesian waters contain on 

 an average about 40 grains to the gallon (in the combined 

 form). 



Oummings, it may be noted, has given reasons for ascrib- 

 ing the sodic carbonate waters in the limestones of Montreal 

 to the numerous bostonite dykes which are often directly 

 associated with the supplies. Suess has discussed the 

 hypogene nature of the mineral waters with free C0 2 along 

 the borders of the Erzebirge, while Parkinson 1 has con- 

 sidered the soda deposits of Lake Magadi in B. B. Africa, 

 as having been formed by the hot springs rising through 

 the alkaline lavas, the water being regarded as of plutonic 

 origin. 



1 Joum. Roy. Geol. Soc, vol. 44, p. 33, 1914. 



