PROCEEDINGS OF SECTION C. 463 



now at a maximum of glaciation. In this case we see' that in the 

 Northern Hemisphere the only areas where glaciation is at a maximum, 

 or near a maximum, are Greenland and Spitzbergen respectively, in 

 the parallels of between 60° to 80° and 78° to 80° N. lat. It will be 

 noticed that these latitudes, too, are not far from where the isotherm 

 of 0° C. comes down to or near sea-level. Poleward of this latitude 

 the observations of Dr. Drygalski and others show that the ice sheets 

 are probably slightly waning for want of snow supplies. One might 

 infer from this evidence that the earth has quite recently passed through 

 a warmer climatic period than that which it at present enjoys. During 

 the climax of such a period the isotherm of 0" C. in the Northern and 

 Southern Hemispheres would have been poleward of its present position, 

 and under these circumstances the poles would receive a larger supplv 

 of snow than they do now, while areas near the Arctic and Antarctic 

 Circles would receive a smaller snow supply than at present. Under 

 these circumstances, too, areas of the earth above the perniinent 

 snow line, situated equatorwards of the Arctic and Antarctic Circles, 

 would have their glaciers and snowfields, relics of the Great Ice Age, 

 diminished with comparative rapidity. As this last interglacial epoch 

 slowly passed away, and save place to slightly colder conditions, ob- 

 viously the isotherms of 0° C. would move equatorward, carrying with 

 them the zone of maximum snow precipitation to about the present 

 latitudes of the Balleny Islands, Greenland, and Spitzbergen ; the 

 snowfall near the poles would be diminished, while that of areas above 

 the permanent snow line, situated in temperate or tropical regions, 

 would be slightly increased. Such an increase, however, in such regions 

 would not necessarily lead at all to an advance of the glaciers ; it might 

 simply lead to the glaciers wasting away in such areas more slowly 

 than they did at the chmax of this last assumed interglacial epoch. 

 According to this view, therefore, the world has quite recently passed 

 the chmax of an interglacial epoch, and is now on its way towards 

 another glacial epoch, an epoch which is to form one phase amongst 

 the many phases of what is commonly known as the Great Ice Age. 

 The Great Ice Age, according to the estimates of Professor A. P. Cole- 

 man, probably lasted for from 100,000 to 150,000 years, even 200,000 

 years. According to various very reliable authorities the last retreat 

 of the ice sheets took place only from 15,000 to 20,000 years ago. In- 

 asmuch as this period of 100,000 to 150,000 years was made up of several 

 glaciations, divided by at least one interglacial phase, each occupying 

 periods of time somewhere about 10,000 to 20,000 years, it cannot 

 obviously be said that the world is already out of its Great Ice Age. 



In Permo-Carboniferous time, as already stated, no less than 

 2,000ft. of glacial and associated strata were deposited, only about 

 150ft. of such strata were formed on the average during so much of 

 the Pleistocene Ice Age as the earth has already experienced. If, 

 therefore, this Pleistocene and recent Ice Age is to be comparable at 

 all in its duration to that of Permo-Carboniferous time, and if the 

 thickness of strata deposited is any index as to approximately how 

 long that time should last, the ratio of the thickness of the Pernio- 



