Trans. N. V. Ac. Sci. 92 April 14, 



amount of the gas or vapor, a very great number of decrements will 

 be needed to produce any sensible effect ; then a less number, and so 

 on, until toward the end, when the decrement needed will be small 

 and the effect comparatively large. Hence temperature changes 

 should have been at first, and for a long time, very slow, and after- 

 ward much more rapid. All we know about what did occur is de- 

 rived from the study of the plants and animals and noting what 

 changes occurred among them ; the results of such study appear to 

 be in harmony with what we should expect. The peculiar life of the 

 Paleozoic lasted several times as long as that of the Mesozoic, and 

 that several times as long as the peculiar life of the Tertiary, and 

 in the Tertiary itself the changes were most rapid of all. 



It is also very suggestive that while the changes in the plants and 

 animals in the earlier periods were world-wide, the changes in the 

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

 were settling down from the poles toward the equator. This was to 

 have been expected if the early polar warmth was due to that " warm 

 blanket." If this was growing thinner, it might be long before any 

 sensible effect was produced ; but when it did appear, it would first 

 manifest itself near the poles, where so much depended upon the 

 heat's being retained. 



With this in view, there is no difficulty in seeing why the flora of 

 temperate America and of Europe and Asia should have their origin 

 in very high latitudes, since, while light and actinic force were always 

 fitted for them, it was there a temperature first appeared which was 

 adapted to their needs. 



The amount of carbonic acid possible in the atmosphere without 

 destroying life is not known, but according to Prof. Remsen of Johns 

 Hopkins University, present animals can breathe an atmosphere 

 containing five per cent, of that gas, " without experiencing serious or 

 even disagreeable effects." This is one hundred and fifty times, and 

 more, the present amount. With animals specially adapted to it, I 

 see no reason why the quantity might not in those days have been 

 very much greater than five per cent. 



The Glacial Epoch, and the siib sequent Warmth. 



The "warm blanket" having been so greatly reduced, the per- 

 pendicular axis was permitted to produce its natural effect, and the 

 climate " became less genial than now." The cold, moreover, was 

 intensified by high latitude uplifts. We may get some idea of the 

 result if we imagine New York State, for example, elevated to a con- 

 siderable height, and if the sun never rose any higher than it now 

 does on the 21st of March. All present vegetation would die out, and 



