580 THE GEOLOGY OF THE WARRUMBUNGLE MOUNTAINS, 



(1) The springs show no evidence of being caused by steam- 

 pressure, for none of them are warm; and volcanic activity has 

 long been extinct in the region. 



(2) Gas-pressure can hardly account for them in a primary way. 



(3) Hydrostatic pressure cannot explain the phenomenon, for 

 we get permanent springs on very high summits. They cannot 

 be connected with tlie artesian system, inasmuch as they are 

 above the artesian intake beds. 



(4) Pressure of overlying rocks is a plausible explanation in 

 some cases where the springs issue from sandstone beds under- 

 lying an igneous mass; biit the increased flow in drought time^ 

 and the occurrence of springs on volcanic summits are facts 

 which cannot be thus explained. 



It seems to me that several of the above causes are in opera- 

 tion, but they are not the primary cause. The primary cause of 

 these remarkable elevated springs is rock-decay. It is a well- 

 known fact that most rocks contain, included in them, several 

 times their own volume of gas, chiefly carbon dioxide and 

 hydrogen, occluded in minute, ultramicroscopic cavities. In the 

 same way they contain water. Decomposition liberates these 

 substances; and in this way the gas-pressure necessary to force 

 up deep-seated waters is produced. 



In rock-formations like those of the Warrumbungles, rock- 

 decay is particularly likely to produce great gas-pressure, inas- 

 much as the elements calcium, magnesium, and iron are not 

 present in large quantities for the liberated carbonic acid to 

 combine with. The most abundant rocks of the region are 

 rather acid trachytes, highly alkaline and very low in lime, and 

 highly siliceous sandstones and conglomerates. The latter are 

 derived from older granitic rocks, and the quartz-veins are 

 therefore, in all probability, studded with gas-pores. Most of 

 the gas produced in disintegration of the rock must therefore 

 escape. 



In a prolonged drought joint-cracks widen, giving increased 

 facilities for the atmospheric air to penetrate into the rocks. 



