CH. XIV] PALAEOBOTANICAL STANDPOINT 145 



versal destruction, must be the effect of dying out. It seemed 

 that some all-embracing, inevitable, cause — "dying out" — must 

 be at work, which in time would kill everything; "killing out" 

 must be more localised and more discriminating. If due to 

 climate, it might act in one region, if due to disease, upon one 

 species, but not in regions far apart, or upon so many species. 



Yet, with further consideration, the problem appeared 

 differently. It had to be taken into account that the mere fact 

 of age means so many more chances of destruction. Therefore 

 these older forms must have suffered far more vicissitudes, and 

 have been subjected to far more numerous attacks from exter- 

 minating agencies than the newer. The lapse of time since the 

 deposition of the Eocene basalt of Antrim has been the subject 

 of investigation by Lord Rayleigh, F.R.S. Basing his calculation 

 on the amount of helium as compared with radium (and hence 

 of uraniiun) present in haematite iron of that age, he reached 

 the conclusion that the interval is one of 30 million years. 



We must acknowledge that the vicissitudes of 30 million years 

 are quite beyond the powers of our mind to grasp, and it seems 

 possible that they may have furnished ample cause, through 

 disease or other adverse conditions, to bring about all the 

 destruction to which paleobotany bears witness. 



There is very strong evidence to show that the whole European 

 branch of the Chinese-North-American flora was killed out. by 

 being subjected to cold which it could not withstand, with no 

 possibility of escape: and that it perished, trapped between the 

 cold of the north behind, and an impassable trans-continental 

 barrier of mountains and seas in front. 



What of the other two branches, the living ones? Has there 

 been extermination of species there? And if so, how has it 

 occurred? We have already gained some knowledge on this 

 subject, by comparing some of their species with those of the 

 European Pliocene — which it must be remembered are nearer 

 in time to the ancestral forms, even if they be not actually the 

 ancestral forms— and we find that of the few species so com- 

 pared somewhere about 90 per cent, have changed. 



To discover something more of the changes which have taken 

 place, we may compare the living members of this flora >vith 

 what are, without any doubt, the ancestors of some of them. 

 The description of these is to be found in Prof. Nathorst's 

 account of the Post-Miocene flora of Mogi in Japan (78-9). This 

 is the largest of several Post-Miocene floras (mostly very frag- 

 ^ . 10 



