244 DISCUSSIONS IF CLIMATOLOGY. 



too thick at the centre unless he were previously 

 made aware that it represented a thickness of 12 miles 

 at that place. The section, of course, is not intended 

 to represent the actual thickness of the sheet, but to 

 show how liable we are to over-estimate a thickness 

 proportionate to an area so immense. It may here be 

 mentioned that had the section been drawn upon a 

 much larger scale — had it, for instance, been made 

 7 feet long instead of 7 inches — it would have shown 

 to the eye in a more striking manner the thinness of 

 the cap. 



At the close of the reading of Prof. James Geikie's 

 paper " On the Glacial Phenomena of the Long Island," 

 before the Geological Society, in May, 1878, His Grace 

 the Duke of Argyll stated that he doubted whether 

 ice could move on a slope of 1 in 211. But a slope 

 so small as 1 in 211 would give a thickness of seven 

 miles at the Pole. Consequently, we have no alterna- 

 tive but to admit that a slope of 1 in 211 is sufficient, 

 or the cap must be over seven miles thick at the Pole * 



* Prof. J. Geikie writes me as follows : — " I have given the height 

 of the glaciation in the North-west Highlands as 3000 feet or there- 

 about, which taken in connection with the glacial phenomena of the 

 Outer Hebrides, implies a slope for the surface of the ice-sheet of 1 

 in 211, or about 25 feet in the mile. It is not improbable, however, 

 that a more detailed examination of the mainlands may compel us to 

 admit a still greater thickness for the ice-sheet of the North-west — 

 the surface of which may have reached to a height of 3500 feet in 

 Ross-shire. This would yield a slope of 35 instead of 25 feet in the 

 mile. After my paper had gone to press I received, through the 

 kindness of Mr. George H. Cook, State Geologist of New Jersey, a 

 copy of his Annual Report for 1877, in which the slope of the ice- 

 sheet that flowed into the northern part of that State is estimated at 

 34 feet in the mile. Prof. Dana, you will remember, comes to the 

 conclusion that the surface of the ice-sheet attained a height upon 

 the Canadian water-shed of 12,000 feet, on the supposition that the 

 ice sloped southwards at the rate of 10 feet in the mile, — if the slope 

 were greater, the Canadian ice, of course, must have been thicker. 

 The inclination of the ice-sheet in the area of the North Sea I 

 estimate at about 12 or 13 feet in the mile." 



