428 G. R. Wieland — Polar Climate in Time. 



herbaceous, as seen in the arboreal lobelias, the shrubby gera- 

 niums, violets and plantains, and the strange arborescent 

 Compositae of the Hawaiian Islands, affords an instructive 

 example. But the evolution of the main groups of flowering 

 plants having long since taken place, we cannot expect to find 

 in islands, which at most show little more than such changes 

 as have taken place in Tertiary time, evidence of the origin of 

 new orders of plants ; though such changes as are observed, or 

 greater, doubtless often take place after the successful invasion of 

 a new area, or in the case of the destruction of competitors in the 

 old home. Moreover, if, as was always the case in the Arctic 

 regions, the period of rigor was quickly followed by one of 

 extremely favorable conditions coming on, nevertheless, at a 

 rate easil}^ taken advantage of by both plants and animals, 

 races of great strength must quite surely be generated; and 

 likewise new species, to an extent and with a rapidity that can 

 scarcely be estimated on the basis of the fairl}^ static conditions 

 of most islands. As polar changes were mainly governed by 

 the precession of the equinoxes, we know that the time scale 

 was one of 12,934 years for the passing from rigorous to melior 

 conditions and vice versa, throughout the successive periods of 

 high eccentricity. 



SumTYiation. — From the preceding portions of the present 

 consideration and argument, it appears that climatic changes 

 of a character affecting life must in the course of time be of 

 minimum amount at the equator, and increase towards the 

 poles, where the maximum amount of such change occurs. 

 Hence throughout time, the nearer a given locality to either 

 pole, the greater the seasonal vicissitudes to which its life is 

 subjected. Next, the view that the origin of life itself took 

 place at the north (or at both of the poles), was accepted as in 

 all probability the reasonable one, although as mentioned, the 

 bare possibility that there has been a supplementary or an 

 original extra-terrestrial origin of life also requires consider- 

 ation. In either case, should the globe ever have been molten, 

 the conditions making it probable that terrestrial life appeared 

 at the poles, were not due alone to lesser solar heat there but 

 mainly to the mechanical action of heavy lunar tides in the 

 primitive equatorial lava seas. If the globe was never molten, 

 any excessive equatorial heat whatever in the early geological 

 periods would still leave the polar areas the probable early 

 scene of life as at present understood. Attention was also 

 called to the fact that the Paleozoic must have been because of 

 climatic and other reasons, such as the freer circulation of 

 oceanic waters, and the greater number of aquatic animals, 

 and lowly organized or spore-bearing plants, a period mainly 

 of generalized origins. Hence, there can be slight strati- 



