PROBLEM OF THE GREAT AUSTRALIAN ARTESIAN BASIN. 175 



below the top of the casing. Is gas still being evolved, and, 

 if so, is it in lesser volume? Without a number of careful 

 observations on this point, there would always be doubt 

 whether the gas was falling off owing to reduction in the 

 flow of the water or vice versa. 



Irregularities of flow due to outbursts of gas have been 

 noted in a few bores in Queensland, e.g., Congoola Lease, 

 Westlands No. 1, and Maria Greek, the latter being outside 

 the Basin though. 



(2) Rock Pressure. — Gregory 1 has claimed rock pres- 

 sure as an agent in artesian flow, a point disputed entirely 

 by Pittman. 



With a stratum of coherent sandstone it is obvious that 

 only when the pore-spaces suffer reduction in volume by 

 some external or internal action, could additional com- 

 pression be exerted upon their water content. This might 

 be brought about by (a) earth movements, involving a 

 reduction in pore-space, (b) shaking of the grains into 

 positions involving closer packing, and (c) solution of the 

 matrix and crumbling of the rock. Of these, (a) is zero, 

 owing to absence of lateral compression since the Basin 

 was filled, (b) may have been brought about by seismic 

 shocks — (note King's 2 remarks anent the level of a well 

 affected by the passing of a train) — and (c) may quite likely 

 be due to the action of the hot alkaline waters upon the 

 felspar grains and clayey matrix of the sandstones; observe 

 that the waters in South Australia may carry solub'e 

 silicates, while the quartz grains of the beds in the Goyder's 

 Lagoon bore have been slightly corroded. 



In this way a cellular porous rock could be formed that 

 would squeeze down slightly under the weight of the cover, 



1 Journ. Roy. G-eogr. Soc, vol. 38, p. 175, 1911; Economic Geology, vol. 

 9, p. 768, 1914. 



2 U.S.G.S. 19th Ann. Kept., pt. n, p. 278, 1898. 



