THE POLAR GLACIERS. 181 



was of the greatest extent and severity. Ten cycles back about 

 210,000 years ago one of the periods of maximum eccentricity had 

 just commenced, the highest since four times that number of years. 

 The perigee, or nearest approach to the sun, happened then as now, a 

 few days after the winter solstice of our half of the world. It was 

 the great summer of the northern hemisphere. But over the south- 

 ern hemisphere at this time, almost if not quite to the tropics, ex- 

 tended one vast sheet of ice. It reached far into Brazil, it covered 

 Southern Africa, and lapped over on Australia. The marks are all 

 there, scored on the solid rocks, to show how it crept up the south- 

 ern slopes of the hills, and how far it pushed its icy arms. In South 

 America at least there is ample proof that the great glacier spanned 

 the southern ocean to reach it ; for the furrows on the rock-beds of 

 Patagonia are from the pole toward the equator, whereas in any other 

 case they would have been from the mountains to the sea. With 

 such a state of things at the southern end of the world, with proba- 

 bly miles in depth of ice and sea in its higher latitudes, there could 

 have been but little water left for the opposite northern regions. 

 What is called the Atlantic-cable plateau, between Newfoundland 

 and Ireland, was very possibly the north shore of the Atlantic Ocean ; 

 and probably no considerable bodies of water existed anywhere north 

 of that parallel. The present continents were all mountain table- 

 lands, far from the vicinity of evaporating surfaces. Like all such 

 elevated regions not exposed to specially moist winds, they were 

 doubtless dry and arid deserts. However warm may have been the cli- 

 mate of the north temperate and arctic zones during this their great 

 summer, their great elevation and the want of any kind of water-sup- 

 ply must have made them barren of all forms of animal or vegetable 

 life. Consequently there would be, as is notably the case, but few if 

 any traces of this part of the great season left in the geological rec- 

 ords, at least above the present seas. 



Five thousand years pass, and the perigee has advanced to meet 

 the vernal equinox. The spring season is now the shortest of all ; 

 but, as the autumnal is correspondingly lengthened, the average cli- 

 mate is about that of the present time. But it is the season of the 

 great thaw the breaking-up time of the southern hemisphere, and 

 the waters are returning to fill the northern ocean-beds. Impercep- 

 tibly a permanent white cap begins to fasten itself to the heights of 

 the boreal zone, to extend its outline, and to increase its depth. Slow- 

 ly the lands are being submerged and the oceans broaden out, till 

 there comes a time when land and water are equalized in the two 

 hemispheres, and the climates are substantially alike. 



Another 5,000 years pass, and the perigee now coincides with 

 the summer solstice of the northern hemisphere. This is the po- 

 sition there of greatest cold : the winters are twenty-eight days lon- 

 ger than the summers ; and the extra days are in great part those 



