MISCELLANEA. 597 



signed. Unfortunately, however, the utmost uncertainty still prevails 

 both in regard to the size of the ice-sheet and also in regard to the 

 actual extent of the submergence. All that we can therefore do, is to 

 make a rough estimate of what probably was the thickness and ex- 

 tent of the ice, and then to ascertain whether the amount of the 

 submergence theoretically deduced from the supposed quantity of 

 the ice, is anything like an approximation to the generally-received 

 opiuion among geologists regarding the probable extent of the 

 submergence. 



It has been proved by Mr. Jamieson that in some parts of Scot- 

 land the iCe-sheet must have at least been 3000 feet thick. Agassiz 

 thinks that in some parts of North America its thickness could not 

 have been less than a mile. The thickness of the ice in Scandinavia 

 and other parts of northern Europe must also have been enormous. 

 What was the probable thickness of the ice in Greenland and other 

 Arctic regions during the glacial period, we are, I presume, unable 

 to form the least conjecture. But to simplify our calculations, let 

 us assume that it was, say 7000 feet thick at the North Pole, and 

 thatit gi'adually diminished in thickness towards the Equator, accord- 

 ing to a law, into the consideration of which we need not here enter, 

 so that the upper surface of the sheet should curve exactly the same 

 as the surface of the land underneath. The specific gravity of ice is 

 92, and the mean specific gravity of the earth, according to the deter- 

 mination of the Astronomer Eoyal, is 6-56. Hence the specific 

 gravity of the ice-sheet would be to that of the earth as 1 to 7. 

 Consequently, if a sheet of the same density as that of the earth, 

 and 1000 feet thick at the Pole had been substituted in the room of 

 the ice-sheet, it would have produced the same effect. But this 

 would be simply adding 1000 feet to the polar diameter of the globe 

 without increasing its equatorial diameter. But 1000 feet thus 

 placed on one side of the globe which, in the present case, is on the 

 north side, would, of course, shift the centre of gravity 500 feet to 

 the north of its former position, and as the ocean would accompany 

 the centre, there would consequently be a submergence at the North 

 Pole equal to 500 feet. But this is not all ; for at the time that 

 the ice*sheet would be forming on the northern hemisphere, a sheet 

 of equal size would be melting off the southern, and this of course 

 would double the effect, and thus produce a total submergence of 

 1000 feet at the North Pole, and a total elevation of 1000 feet 

 at the South Pole. A sheet 3500 feet thick at the Pole would pro- 

 duce one-half that effect. 



