THE AGE OF ICE. 837 



feet in thickness, and a displacement of the earth's center of gravity 

 one mile toward the north at the height of the glacial age. In fact, 

 it is not necessary to assume any such amount of displacement. If 

 the earth's center of gravity coincided with its center, so as to equal- 

 ize the amount of water in the northern and southern hemispheres, 

 Itasca Lake would not be more than 600 feet above sea-level. Now 

 push the center of gravity 2,000 feet toward the north, and the Arctic 

 Ocean would be so much deeper over the pole, and the water would be 

 about 1,000 feet deeper at the latitude of 45. To accomplish this re- 

 sult, we must calculate that the space within the Arctic Circle was 

 covered by an ice-cap averaging perhaps 8,000 feet in thickness an 

 entirely supposable case. Such an amount of displacement would 

 flood all the low lands of North America down to the line of 40, and 

 fully satisfy all the conditions of the problem. 



It thus seems probable that there have been many glacial periods 

 in each hemisphere, and that the ocean, like a mighty pendulum, vi- 

 brates from pole to pole through vast but regular periods. It is not 

 necessary to suppose a cataclysm at the end of each period, as some 

 of the earlier writers did ; but rather, an insensible drainage of waters, 

 which so gradually submerges the lands and pushes the human race be- 

 fore it, as hardly to be perceptible in the course of generations ; ever 

 uncovering new continents, and opening up fresh fields and pastures 

 new to human industry, when the old are exhausted. 



The southern hemisphere is now undergoing the slow refrigeration 

 of its long winter. This began about 6,500 years ago ; it will end 

 about the year 4,870. It has passed its middle, but not its culmina- 

 tion, even as the greatest average cold of our ordinary winter is nearer 

 the vernal equinox than the winter solstice. It is probable that, 2,000 

 years from now, the southern continents will be still more deeply del- 

 uged ; the Antarctic ice-cap will have extended several hundred miles 

 to the northward, and the glaciers which have already appeared among 

 the Andes will have covered the plateaus of Patagonia and Chili. 

 Nevertheless, we need not expect that mankind will then witness the 

 utmost possible degree of refrigeration, because the ellipticity of the 

 earth's orbit is now less than it has been at certain periods in the past, 

 and will be again in the remote future. 



I feel that, in this discourse, I have ventured upon doubtful and 

 perilous ground. Nevertheless, however illogical and imperfect my 

 conclusions may have been, I feel certain that herein is the key to the 

 mystery. I leave the question, trusting that abler minds may be 

 directed to its consideration and solution. 



