234 DISCUSSIONS IN CLIMATOLOGY. 



thinner it should be, and that this is perfectly suffi- 

 cient, as has already been stated, to account for the 

 decrease in the thickness of the layers from the top 

 downwards, without assuming any of the ice to have 

 been removed by melting or by any other means. 



Continental Ice radiating from a Centre of Dis- 

 persion must be Thickest at the Centre, and gradually 

 Diminish in Thickness towards the Circumference. — 

 Whatever theory we may adopt as to the cause of the 

 motion of ice, it will follow as a necessary consequence 

 that the sheet must be thickest at the centre and 

 thinnest at its edge. In a continental sheet like that 

 covering the Antarctic regions, we are not warranted, 

 as has already been noticed, in assuming that the sur- 

 face of the ground under the sheet slopes persistently 

 outwards from the centre or Pole to the edge ; in other 

 words, we cannot infer that the Antarctic ice, like an 

 ordinary glacier, rests on an inclined plane. 



Now, if we adopt the generally accepted theory, 

 that gravity is the force impelling the ice forward, 

 we must assume the sheet to be thickest at the centre ; 

 for unless it were so, gravity could have no tendency 

 to produce motion, because the force which moves the 

 ice must not only act horizontally, but act more in 

 one direction than in another ; and this it could not 

 do were the ice of uniform thickness. Were the sheet 

 of this uniform thickness, the forces acting on it 

 would balance each other, and no motion could result. 

 If the sheet is to be forced out horizontally along the 

 flat surface by its o%vn weight, then there must be a 

 piling up of the ice in the interior. If the ice comes 

 from the centre, then the pressure must be greatest 

 there ; but in order to this, the sheet, of course, must 

 be thickest at the centre. 



Supposing it should be asserted that it is not the 



