PROBLEMS OF THE ARTESIAN WATER SUPPLY OF AUSTRALIA. 133 



Several objections to the theory that flowing wells are 

 due to rock pressure suggest themselves. In the first place 

 the effective pressure at any given point in the porous beds 

 will be less than that due to the total weight of the overlying 

 rocks, because on account of the cohesion of these rocks, 

 and the continuity or lateral extension of the beds, they act 

 more or less like the arch or girder of a bridge. The weight 

 of the overburden at any point would not be completely 

 felt until a depth had been reached where the rocks were 

 in a plastic state. 



If a single brick be knocked out of the lowest course of 

 a high wall, the weight of the wall will not close up the 

 space left by the brick, because of the cohesion between 

 the bricks and mortar, and because, in the different courses, 

 the bricks are laid "breaking joint." If the bricks w T ere 

 laid accurately and vertically over one another, and without 

 any mortar, the space caused by the withdrawal of one 

 would be immediately filled by the fall of all the overlying 

 bricks. 



Then again, if the pressure on a porous bed be sufficient 

 to squeeze out the water when the bed is intersected by a 

 bore, it is evident that the same pressure would have been 

 sufficient to prevent the water from filling the porous bed 

 in the first instance. 



A third argument against the rock pressure theory is 

 that even if it were possible for a porous bed to be first 

 filled with water, and subsequently subjected to the rock 

 pressure suggested by Professor Gregory, the effect would 

 be that the water would return to the surface along the 

 intake area; for the pressure, being vertically downwards, 

 would have a tendency to squeeze the water laterally 

 along the porous bed until it escaped at the surface. The 

 ultimate result of the pressure on the porous bed would be 

 to render it dense and indurated, and it would thus lose its 

 capacity for absorbing water. 



