30 THE POLAR GLACIERS. 



the calculations of Mr. James Croll, about 850,000 years ago. 

 But it is now generally thought that we have no need to go back 

 as far as that for the period of the last glacial epoch. 200,000 

 years ago the focal distance was 10,500,000 miles, and the winter 

 excess was twenty-eight days. This, on the supposition heretofore 

 made of the absolute zero of cold being at least 257 below the 

 freezing-point, would lower the mean temperature in polar 

 regions, 50 Fahr., and would unquestionably extend the perma- 

 nent ice-limits far into the temperate zone. From that time, 

 down to 70,000 years ago, the eccentricity was continually from 

 two to four times greater than now. Since about 70,000 years 

 ago, it has been nearly all the time less than at present. Thus 

 it may fairly be concluded that the great glacial period of the 

 Post-tertiary era carne to an end with the fourth secular winter 

 in the past, or B. c. 67,000. 



This is a very interesting date to us of the genus homo / for 

 it must have been about this time, according to all accounts, that 

 our forefathers made their appearance on the earth. Man, with 

 the long-haired mammoth, the woolly rhinoceros, the huge cave- 

 bear, the great-horned reindeer, and numerous other species now 

 extinct, followed close upon the retreating ice-fields of the 

 bowlder period. Our primeval ancestors were a race of hunters, 

 and they subsisted on the most abundant and magnificent game 

 that the world has ever seen. They lived in caves or under pro- 

 jecting ledges, and with only flint-headed w r eapons contested 

 their lives and homes with savage beasts. They cracked the 

 bones of animals for their marrow, or crushed them in stone 

 mortars for the fats and the juices which they contained. It 

 was the lingering carnivorous instinct to gnaw the bones of their 

 prey. They .had fires at their funeral feasts, but there is little 

 evidence of their indulging often in the luxury of cooked meats. 

 It was a rude life, and a hard struggle they must have had for it ; 

 but their history is read in the drift-beds and cave-deposits of 

 Europe, as plainly as if there had been a Herodotus to write it. 



The effect and bearing of the great ice periods on geological 

 work and time will be further considered in a second article in 

 continuation of this. 



