146 ALEX. L. DU TOIT. 



little has been said, but it seems not unlikely that there is 

 a general thinning out of the Jurassics in those directions, 

 and that to the east, on the contrary, still lower zones are 

 involved equivalent to the Lower Jurassic, Rhaetic and 

 even the Upper Triassic without any unconformity, depo- 

 sition having commenced in the east and the area of sedi- 

 mentation having gradually extended westwards. An 

 overlap like this, such as might only be expected in view 

 of the huge area covered, is indicated by the zones present 

 between Toowoomba and the sea-coast, which include 

 horizons certainly lower than the artesian beds proper, or 

 the Walloon Series on the top of the plateau; such a 

 transgression is in fact shown in Cameron's section through 

 Cloncurry and Hughenden. 



This relationship would be reflected in the position of 

 the water bearing zones relatively to the base of the 

 Artesian series, and it is significant that away from the 

 margin the former are commonly situated not far above 

 the base of the group (See II. pis. 16 - 21), but closer to the 

 *' intakes" there are considerable thicknesses of non-pro- 

 ductive strata below the main water-bearing horizon, as 

 for example, in Greendale Resumption (Tambo), Mucka- 

 dilla, Roma, and perhaps Nevertire near Warren. Indeed, 

 under such conditions, it would be uneconomical, despite the 

 value of the geological information obtainable, to sink the 

 boreholes down to bed-rock, as has consistently been carried 

 out in New South Wales during late years. Probably this 

 condition holds over a great length of the eastern margin 

 where the Jurassics or Jura-Trias rest with unconformity 

 upon granite and palaeozoic beds, e.g., Dawson River. 



Whether there may not also be a lateral change east- 

 wards into less pervious sediments is not clear, but such a 

 possibility would help to explain the failure of deep boring 

 near Brisbane, for, in spite of Pittman's criticisms based 



