PROBLEM OF THE GREAT AUSTRALIAN ARTESIAN BASIN. 197 



regards the waters as possibly of magmatic origin ; their 

 chlorine content is invariably low. 



Ever since the pioneer work of Bischoff, geologists have 

 recognised that in the waning stages of volcanicity 00 a , 

 •N, and H 2 0, are given off at low temperatures, for example 

 in Java, in the mofettes of the Eifel, etc., and it may not 

 unreasonably be surmised, that in Australia these gases 

 were set free, both below ground as well as at the surface, 

 so that a large proportion of the 00 2 required for the car- 

 bonation of the artesian waters could have been derived 

 from such volcanic sources. 



It is worthy of note that the Ooonamble area, adjoining 

 the Warrumbungles, is specially characterised by the 

 presence of free 0O 2 in its waters. 



That such evolution of 00 2 has not wholly ceased, is 

 indicated by the existence of certain warm springs with 

 free carbon dioxide, outside the eastern limits of the Basin, 

 but still within the region of volcanic activity, e.g., the 

 Einasleigh (180° P.) Oakvale (hot) and Innot Springs (158° 

 - 168° F.) between Georgetown and Herberton in Queens- 

 land, rising in a tract of granite, gneiss and metamorphic 

 rocks, and the tepid spring at Rock Plat near Oooma in the 

 extreme south-east of New South Wales, issuing from 

 Devonian strata overlain by basalt. The close association 

 of all four with basalt may be regarded as evidence for the 

 volcanic origin of these thermal springs, and Jack 1 has 

 connected the first and third with the younger phase of 

 volcanicity. 



While alkaline carbonates exist in all four waters, they 

 predominate in the second and fourth, the ratio of this salt 

 to the sodic chloride being respectively 1:2, 5:1, 1 : 2*5 

 and 8 : 1. 



1 Jack and Etheridge, The Geo!, and Palaeont., Qld., pp. 586, 626, 1892. 



