22 Thickness of the Antarctic Ice , and its [January, 
dispersion is the centre of the sheet. In the case of the 
Antarctic sheet the centre of dispersion cannot, however, 
be far from the Pole, and the Pole in all probability is not 
far from the centre of the sheet. We may therefore in our 
inquiry safely assume the Pole to be the centre of dispersion. 
It is obvious that, if the Antarctic ice be radiating in all 
directions from the Pole as a centre, a portion of a layer 
which in say latitude 85° covers 1 square foot of surface 
will on reaching latitude 8o° cover 2 square feet. At latitude 
70 it will occupy 4 square feet, and at latitude 6o° the space 
covered will be 6 square feet. Then if the layer was 1 foot 
thick at latitude 85°, it would be only 6 inches thick at lati- 
tude 8o°, 3 inches thick at latitude 7 o°, and 2 inches at 
latitude 6o°. Had the square foot of ice come from latitude 
8g° it would occupy 30 square feet by the time it reached 
latitude 6o°, and its thickness would be reduced to i-30th of 
a foot, or 2-5ths of an inch. 
Now the lower the layer the older it is, and the greater 
the distance which it has travelled. A layer near the bottom 
may have been travelling from the Pole for the past 10,000 
or 15,000 years, whereas a layer near the top may perhaps 
not be twenty years old, and may not have travelled the 
distance of a mile. The ice at the bottom of a berg may 
have come from near the Pole, whereas the ice at the top 
may not have travelled 100 yards. It follows therefore that, 
other things being equal, the lower a layer is the thinner it 
should be, and that this is perfectly sufficient 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 Dispersion must 
he 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 surface 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 
