CONDITIONS OF CONTINENTAL ICE. 243 



under-estimating the thickness. We have 

 a striking example of this in regard to 

 the ocean. That which impresses us most 

 forcibly in regard to the ocean is its pro- 

 found depth. A mean depth of, say, 3 

 miles produces a striking impression ; but 

 . if we could represent to the mind the vast 

 g area of the ocean as correctly as we can do 

 ~ its depth, shalloivness rather than d< ^l], 

 •§ would be the impression produced. A sheet 

 £ of water 100 yards in diameter, and only 

 | 1 inch deep, would not be called a deep 

 r f but a very shallow pool or thin layer of 

 | water. But such a layer would be a corrcet 

 ■g representation of the ocean in miniature. 



1 Were we, in like manner, to represent to 

 o the eye in miniature the Antarctic ice-cap, 

 H even as 12 miles in thickness at the Pole, 

 ro . we should call it a tldn crust of ice. The 

 •| mean thickness of the sheet would be about 

 f © 4 miles, and this would be represented by 

 g I? a carpet covering the floor of an ordinary- 

 la sized dining-room. Were those who con- 

 * J . 



g^ sider the above estimate of the Antarctic 



-°| ice-cap as extravagantly great called upon 

 || to sketch on paper a section of what they 

 1 1 should deem a cap of moderate thickness, 



2 5 ninetv-nine out of a hundred would draw 



.s o 



■as one of much oreater thickness than 12 miles 



3% at the centre. 



The accompanying diagram represents a 

 section across the cap drawn to a natural 

 scale, the upper surface of the sheet having 

 a slope of half a degree. No one looking 

 at the section would pronounce it to be 



