Oh. XIII.] 



THE EXCENTKICITIES OF THE OBBIT 



most 



295 



with Mr. Croll, that if the date of the 

 cold can be arrived at by aid of a very large excentricity, it 

 would be a more probable conjecture to assign C than B as 

 tlie period in question. 



Without 



tions of success in chronological speculations of this nature, 

 it mav be useful to take a retrospective survey of some of the 



eoloo-ical monuments viewed m their 



most prominent of the g 



bearing on climate which have been observed in the northern 

 hemisphere, within the period comprised in the above table. 

 We have only to go back 8,000 years before historical times, 

 in order to find the northern hemisphere in that phase of 

 precession when winter occurred in aphelion ; and if, accord- 

 ing to Herschel's estimate, the summers were 12° hotter and 

 the winters 12° colder than they are now, (the excentricity 

 being nearly as moderate as at present,) we might expect 

 to meet with some indications of a difference in climate in 

 the flora and fauna of the earliest Swiss lake -dwellings 



that the date of 



and Danish kitchen-middens, assuming 



any 



of these fell within the era alluded to. 



It 



mi 



therefore be argued that as the wild animals and plants of 



so precisely what they are now, 



Neol 



this Neolithic period cannot date back so far as 11,000 years 



before our time ; and if, as shown by Dove's tables, ana tor 

 reasons already explained, the planet is now warmest in June 

 when the earth is farthest from the sun, the effects of pre- 

 cession in exaggerating the summer heat ought to have been 

 jreat indeed when all this land was presented to the sun in 

 perihelion. Such hot summers would be equally adverse to 

 the hypothesis which would assign so modern a date to the 

 Eeindeer period when, as we have before seen, man co-existed 

 with the last surviving mammoths, and when some other 

 northern quadrupeds extended their range, like the reindeer, 

 to the south of France. If, on the other hand, we were to 



mi 



the excentricity was nearly three times as great as at present, 



a h M -» • i • t *% * . -m * a flit 



demur 



arts and the condition of the caves of that epoch are not 



from those of the Neolithic 



in suDDOsinGr them 



