290 T. W. E. DAVID. 



water into carbonates, and so bringing about their precipitation 

 and removal from the water, if the minerals forming them are 

 hurtful to plant life. Such aeration is effected by allowing the 

 water to flow from the mouth of the bore into a circular tank three 

 hundred feet across and from two to three feet deep. 



The origin of this artesian water in the United States on the 

 east side of the Rocky Mountains is evidenced by the following 

 facts. The rainfall of the Mississippi River Basin amounts to 

 six hundred and twenty cubic miles of water annually. Of this 

 total one hundred and seven cubic miles are annually discharged 

 into the Gulf of Mexico. There remain therefore five hundred 

 and thirteen cubic miles of water to account for. As not more 

 than forty per cent, of the total rainfall is lost by evaporation, 

 about two hundred and sixty-five cubic miles of water out of the 

 total six hundred and twenty cubic miles produced by the annual 

 rainfall must percolate, and so form what the American Geologists 

 term the underflow, undersheet, or phreatic water, which consti- 

 tutes the source of supply for the artesian and sub-artesian wells. 



Artesian Water in Australia. — This is of two kinds, (a) 

 natural, and (b) artificial. 



(a) Natural artesian water rises to the surface in many parts 

 of the east-central portions of Australia from mud or mound springs. 

 These occur chiefly in strata of Cretaceous age. In Lower Cre- 

 taceous time, the eastern portion of Australia, comprising the 

 Oordillera and a strip of country about one hundred miles in width 

 on either side of it, was probably completely isolated by ocean from 

 the Gulf of Carpentaria southerly, either to the Australian Bight, 

 >or to the Coorong Coast near the mouth of the Murray River, or 

 perhaps in both these directions. If the latter was the case a 

 triangular area of older rocks extending from near Mount Browne 

 through the Barrier Ranges to Mount Lofty, near Adelaide, and 

 thence to the Gawler Ranges must have been isolated from Eastern 

 Australia, and so formed a large island between the latter region 

 and West Australia. The question as to whether the Cretaceous 

 Ocean ever extended across Australia to the Coorong, from the 



