GEOLOGICAL CLIMATE IN HIGH LATITUDES. 365 



record of life is such as it would be if the warmth were due to a blanket 

 of carbonic acid and water-vapor, and the temperature fell in accord- 

 ance with Tyndall's law. 



It is also very suggestive that, while, in the earlier periods, the 

 changes in plants and animals were world-wide, the Tertiary changes 

 were more and more confined to high latitudes, as if the cold were set- 

 ting down from the poles toward the equator. Such was the effect to 

 be expected if the early warmth was due to the warm blanket of CO 2 

 and aqueous vapor. If that was growing thinner, it would be long 

 before any sensible effect would be produced ; but, when it did appear, 

 it would first manifest itself near the poles, where less solar heat was 

 received, and where so much depended upon the heat being retained, 

 and from the polar regions it would spread toward the equator. With 

 these facts in view, there is no difficulty in seeing why the flora of 

 temperate or even warmer regions should have had their origin in 

 very high latitudes, since it was there that a temperature first ap- 

 peared which was adapted to their needs. 



I have purposely avoided speaking of how much CO 2 the air can 

 contain and support life. I doubt very much the possibility of say- 

 ing what the limits were in those remote times when not merely every 

 species, but every genus, was exceedingly unlike any now living. They 

 may have been adapted to conditions fatal to any creature known to 

 us. It is certain that as the air grew purer the early animals died, and 

 were replaced by others more like those now living. Present animals, 

 or even human beings, according to Professor Remsen, of Johns Hop- 

 kins University, can breathe an atmosphere containing five per cent 

 of carbonic acid " without experiencing serious or even disagreeable 

 effects." That is, the present amount of CO 3 could be increased one 

 hundred and fifty times, and more, without " even disagreeable effects." 

 If this be true, the fact that the animals of those early times flourished, 

 is no reason why we may not believe that the atmosphere contained 

 many hundred times as much carbonic acid as it does now. 



Accounting for the uniformity of biological conditions, including 

 in that term heat, light, and actinic forces, solves only a part of the 

 climatic problem. The cold which followed must also be accounted 

 for, as well as the return of a mild climate to regions so long covered 

 with ice. The former was a corollary of the causes already discussed. 

 It was due to the combined effect of a perpendicular axis and a purer 

 atmosphere, aided by those high latitude uplifts which occurred at or 

 soon after the close of the Pliocene. The warm blanket being re- 

 moved, the natural effects of an upright axis began to show them- 

 selves. It was the same as if the sun got no farther north than 

 it does now on the 21st of March. Since the cold of the vernal 

 equinox is in part the residuum of winter, it will be near the truth to 

 say that, with the axis perpendicular, the temperature would be the 

 same as now in April. The present flora would die out, and it would 



