14 Evidences of a Glacial Epoch in Victoria 



Therefore we are stimulated to inquire whether the sister 

 sciences can throw any side-lights upon the problem of the 

 post-miocene glaciation of Victoria. 



It appears to me that very valuable aid is available from 

 these sources. 



II. 



• Recent investigations have established the fact that the 

 earth's climate, so uniform in character within historical 

 times, varies very considerably if we take long periods into 

 account. The climate known to man has been shown to be 

 a mean between two extremes of heat and cold which have 

 prevailed during previous epochs. 



Dr. Croll has investigated the subject very fully, and the 

 conclusions which he has formed have been accepted by such 

 men as Archibald Geikie, the Inspector-General of the 

 Geological Survey of Great Britain, and by Sir William 

 Thomson. 



He has shown that the earth's climate at any period 

 depends upon a complex arrangement of circumstances. 

 It is, of course, in the first place, dependent upon the amount 

 of heat sent to it by the sun ; but the effect of this, or its 

 amount at any particular time, is modified by the form of 

 the earth's orbit at that time, by the position of the earth in 

 that orbit, by the precession of the equinoxes, the obliquity 

 of the ecliptic, and greatly by the distribution of snow and 

 cloud on either hemisphere. All these conditions are incon- 

 stant, although they change but slowly. And as their rates 

 of alteration vary they sometimes coincide and augment 

 their effects, whilst at other times they neutralise each 

 other's influence more or less. 



The earth's orbit varies from age to age. At this moment 

 it is losing the elliptic form it had not very long since, geo- 

 logically speaking, and it is becoming more and more 

 circular. The limits of its variations are known. Fourteen 

 million miles is the highest eccentricity to which it attains, 

 and its lowest is about half a million. At the present 

 moment its variation from a true circle amounts to three 

 million miles. The result of this inconstancy is that the 

 seasons, apparently so equally distributed throughout the 

 year, are variable in length from epoch to epoch. The 

 present eccentricity gives to us in the Southern Hemisphere 

 a summer half-year seven days shorter than our winter 

 half-year ; but there have been periods when the difference 



