S4:2 president's address. 



Glacial phenomena are I'eported from various ages between the 

 Carboniferous and Pleistocene Formations, and the phenomena 

 as exhibited in Australia are well set forth in Pi'ofessor David's 

 Address to Section C. of the Aust. Assoc. Brisbane, 1895. 



The most important and tangible of the recorded phenomena 

 in the northern hemisphere are those of the "Great Ice Age," as it 

 is called, in the title of Dr. James Geikie's book. The temperature 

 of the earth, the north pole at least, was cooling down at the 

 end of the Tertiary Period, and the cold culminated in the 

 Pleistocene. Dr. Geikie sa^'s that at least six different periods 

 can be proved during which the cold advanced and retreated, and 

 between which mild conditions prevailed. Other geologists count 

 these to be less in number. 



Various explanations have been given for the spread of Arctic 

 conditions from the pole, the most noted being probably that 

 known as Croll's theory. Dr. Croll argues that the orbit of the 

 earth, in consequence of the varying positions and attractions of 

 the planets, increases in eccentricity at long intervals of many 

 hundreds of thousands of years. The Glacial epoch occuiTed 

 in one of these periods. High eccentricity would, when the axis 

 of the earth was inclined in the line of the major axis of the orbit, 

 cause long mild summers and short winters in one hemisphere and 

 short summers and long cold winters in the other. Under the 

 latter conditions, great cold and accumulation of snow and ice and 

 what is called a glacial period would result. With the precession 

 of the equinoxes, the conditions would alternate in the northern 

 and southern hemispheres till the orbit of the earth lost its 

 extreme eccentricity. 



Major-General Drayson considers that the pole describes a circle 

 round a point 6" from the pole of the ecliptic, so that, 13,700 B.C., 

 the angular distance of the two poles would be such as to bring 

 England within the Arctic circle. 



" Professor G. H. Darwin has considered the possibility of the 

 pole having worked its way in a devious course 10° to 15° from 

 its present geographical position, but points out that such a 

 movement would require extensive surface deformation and shift- 



