the Glacial Epoch in the Northern Hemisphere. 175 



been somewhat greater, owing to the condition of the southern 

 hemisphere at the time. For when the northern hemisphere 

 had attained its maximum of glaciation, the southern hemi- 

 sphere would have lost the ice-sheet in which it, in its turn, had 

 been previously enveloped, and the released waters would have 

 flowed, aided also by the attraction of the northern ice-sheet, 

 from the southern hemisphere into the northern, and have cor- 

 respondingly raised the general level of the ocean in the northern 

 hemisphere above its previous state, and above the state to which 

 it again came on the breaking up of the northern ice-sheet and 

 the gradual re-formation of the ice-sheet in the south. To esti- 

 mate the influence of this cause, we have but to make use of 

 formula (1) in paragraph 2, and integrate from = 0. Then rise 

 of the ocean from this cause 



= - (0-1446 cos 6 + 0-0479 cos 2d + 0-0081 cos S6)h. 



In latitudes 45° and 60°, 0=135° and 150°; and the rise 

 of the ocean level = 00965 A and 0-1042A feet, if h be expressed 

 in feet, and the material be rock, or 0-0322A and 0*0347 h feet, 

 if the material be ice. Putting A = 7000 feet, these become 225 

 and 243 feet. 



6. It is evident that the southern ice-sheet is at the present 

 i me only very partially formed, and therefore cannot produce 

 results near so large as those obtained in the last paragraph in 

 lowering the present sea-level in the northern hemisphere. 



Nor is it to be supposed that when the glaciation in the 

 northern hemisphere was at its maximum, the ice-sheet reached 

 down so far as the equator. The results obtained in paragraph 

 4 must therefore be somewhat diminished on this account. 



We may put the change of level of the ocean in latitudes 45° 

 and 60° north at, perhaps, 650 and 1000 feet. 



7. But there is a circumstance well w T orth considering, which 

 may have considerably increased these during the Drift Period. 



I have shown that if the ice-sheet was a part of a hemisphe- 

 rical shell of thickness 7000 at the pole, and becoming thinner 

 towards the equator, but stopping short in some latitude (say 

 30° or 35°) before reaching the equator, the difference of level 

 of the ocean in latitudes 45° and 60°, in any opening connected 

 by a channel, however narrow, with the unfrozen ocean about the 

 equator, now and at the time of greatest glaciation in the north- 

 ern hemisphere, may be taken at 650 and 1000 feet. The 

 thickness of the ice in these latitudes would be 3500 and 5250 

 feet; that is, half and three-quarters of the thickness at the 

 pole, because the thickness varies as the square of the sine of the 

 latitude. 



Now, as the ice-sheet began to melt and break up into por- 



