56 Primitive Man. 



that the difference between the greatest and least distances 

 from the snn has been between lour and tive times as great 

 as at present. That is, instead of being, as now, a differ- 

 ence of only 3,000,000 miles, it was from twelve to fourteen 

 millions. Furthermore, owing to what is known to astron- 

 omers as the precession of the equinoxes, at regular intervals 

 of 10,50t) years the winter season has occurred and will occur 

 when the earth is in aphelion, or at the longest distance from 

 the sun. If, now, these two events concur, that is, if the 

 greatest eccentricity of the earth's orbit hai)pens at a time 

 when winter occurs in aphelion, the earth would be in mid- 

 winter at ninety-eight millions of miles distance from the 

 sun, instead of, as at present, ninety-one millions, and the 

 "Winter would be twenty-six days longer than Summer, 

 instead of, as now, being eight days shorter. 



Working upon these data, Prof. Croll asserts that the 

 first of these periods of great eccentricity began 2,650,000 

 years ago, and lasted 200,000 years ; the second began 

 880,000 years since and lasted 160,000 years; the third 

 commenced 240,000 years ago and lasted 160,000 years. 

 This would give us, since the termination of the last glacial 

 era (or eras), 80,000 years. But it is certain that man 

 of the river-drift period lived in pre-glacial times, and if 

 Ave accept the conclusion that the most recent glacial era 

 commenced 240,000 years ago, we must allow not less than 

 400,000 years ago as the date of the close of the Pliocene 

 period, and the probable first appearance of man. Other 

 theories which have been proposed to account for the 

 Glacial Age, such as variations in the intensity of solar 

 radiation, the movement of the earth from a colder into a 

 warmer region of space, alteration in the axis of the earth 

 and others, are fully stated and criticized in the twelfth 

 chapter of Sir John Lubbock's '' Prehistoric ]\lan," as are 

 also investigations into existing deposits and formations 

 with a view to ascertaining the probable antiquity of the 

 stone and bronze ages. 



With the disa})pearance or final retreat northward of 

 the cave men, now represented as seems probable, if they 

 have left any descendants, by the Esquimaux tribes alone, 

 me may say that the palaeolithic age as a generally ])revailing 

 stage of ])rimitive life closes, and we observe the gradual 

 appearance of the ground or polished stones which typify the 



