Mr. J. C. Moore on Glacial Submergence. 373 



First, let us suppose that the ice is obtained at the expense of 

 the sea ; in other words, suppose that the quantity of ice at the 

 south pole, when the north is under glacial conditions, is the same 

 as at present. The cap extends to lat. 35°, where, by Archdea- 

 con Pratt's law, it will be 3290 feet thick. Calling the earth's 

 surface 1, this area will be = 0*2132; and if three-fourths of the 

 remainder, or *59, be sea, S= the depression of the sea, A'= the 

 mean thickness of the ice-cap, then 



8 x 0-59 = h' x 0-2132 x 0-92, or S=±h ! . 



The total quantity of ice forming the cap is —tto* xhx cos 2 lat., 

 which, taken from lat. 35° to the pole, =7r« 2 xhx 0*671, whence 

 I deduce the mean thickness h f =hxO'7S7. 



If we take h = 7000 feet, the assumption of Mr. Croll and of 

 Archdeacon Pratt, h!= 5500 feet, and 8 = 1833 feet. Archdeacon 

 Pratt has shown that a thickness of 7000 feet at the pole would 

 produce an elevation of the sea equal to 1000 feet at lat. 60°; 

 and as it appears that the drain on the sea would lower it 1833 

 feet, the result is a depression of 833 feet. 



Let us now suppose that all the ice is supplied by the melting 

 of that at present in south latitudes. The quantity required to 



produce a submergence of 2300 feet is x 2300, or 16,100 



feet of ice at the pole, which, by Archdeacon Pratt's law, will be 

 thinned out to 5300 feet at lat. 35°. 



Sir James Ross sailed for hundreds of miles east and west in 

 latitudes higher than 70°. The ice-barrier in lat. 76° and 78° 

 was under 200 feet. The valleys near Mount Herschel are said 

 to be filled with snow several hundred feet thick. If we allow 

 all the Antarctic regions down to lat. 70° to be covered by a 

 uniform cap of ice 2000 feet thick, I think it will be admitted 

 that this is an exaggerated estimate of the existing ice. A simple 

 calculation will show that such a cap, covering, as it does, only 

 0-06 of the surface of the globe, would not supply the twentieth 

 part of the ice required. 



It appears to me, therefore, that this theory, however tempt- 

 ing, must be abandoned. 



As the quantity of ice to be supplied by the melting of that at 

 the south pole is so greatly disproportionate to its object, it is 

 unnecessary to discuss what appears to me to have been too lightly 

 assumed — viz. that when one pole is under glacial conditions, the 

 opposite will be entirely free from ice. 



Phil. Mag. S. 4. Vol. 31. No. 210. May 1866. 2 C 



