108 T. S. JEms— Windings of Hi vers. 



It is not possible in the limits of this paper to adequately discuss 

 questions which, as we know in the case of the artesian waters of 

 Central Australia, have given rise to such diverse opinions among 

 well-kTiown professional geologists who have made long and special 

 studies of the subject. It will readily be admitted that the ordinary 

 explanation of the origin and flow of artesian wells in regions of 

 moderate or abundant rainfall, situated in well-defined basins where 

 the exact position, extent, and absorbing capacity of the water-table 

 outcrop can be carefully determined, may be entirely inadequate to 

 account for the flowing wells of vast arid regions like those of 

 Australia and Africa. 



It is moreover almost incredible that, where the outcrop of the 

 water-bearing strata is so remote from the wells themselves and the 

 dip over the intervening country so slight, the rise of the water could 

 be due to direct pressure of water flowing downwards through the 

 higher portions of the beds, unless on the supposition of the existence 

 of large and continuous open fissures. Local pressure arising from 

 variation in the level of the water-table in adjacent areas might, 

 however, quite conceivably be adequate to account for the phenomenon, 

 especially if assisted by the presence of large volumes of gas under 

 compression. Much stress has been laid by Gregory and other writers 

 on the pressure of the overlying strata,' but if this were sufiicient to 

 squeeze water from the pores and crevices of a bed and force it up 

 through hundreds of feet to the surface as soon as a free passage was 

 provided, surely the same pressure would have long ago obliterated all 

 such pores and prevented water from ever having obtained access to 

 the bed in question. 



The points to which attention should be directed as likely to throw 

 light on the origin of the oases artesian wells are : the area and 

 position of the outcrops of the impermeable grey shales and the 

 underlying sandstone, and their relations to possible sources of water, 

 whether rain, river, or lake ; the nature of the bed of the swaTup 

 region of the upper Nile ; the amount and distribution of the rainfall 

 of all surrounding regions : the amount of water lost in different 

 reaches of the jNile over and above that which can be directly 

 accounted for by evaporation and by water abstracted for purposes of 

 irrigation ; the total thickness of the water-bearing sandstones, and the 

 presence or absence within them of impervious strata ; and lastly, the 

 relation of the water-bearing beds to the underlying crystalline rocks. 



V. — Windings of Rivers. 



By T. S. Ellis. 



rPHE course of rivers cannot be properly understood if regarded as 

 JL objects complete in themselves. In reality, a river is only a part 

 of a sj'stem of channels serving to drain the whole of the area over 

 which it extends, the breadth as well as the length. Of this system 

 the ti'ibutaries are an essential part. So, too, valleys and combes 



' J. W. Gregory : " The Dead Heart of Australia," Louilou, 1906, pp. 288-289. 



