940 



SCIENCE 



[N. S. Vol. XXX. No. 783 



warm mantle of vapor and cloud hypo- 

 thetieally clothed the whole earth, and 

 even half way down the geologic ages was 

 thought to have enshrouded the globe and 

 to have given warm, sultry climates to all 

 latitudes. But this mantle at length was 

 made to give place to rifted clouds and 

 clearer skies, and later on to mild aridities 

 followed at length by desert stages which 

 are even now supposed to be creeping out 

 persistently on the once fertile lands. 

 Thus we reach our own times at a putative 

 stage when heat and air and moisture are 

 running low; thus the predestined end is 

 foreshadowed in the not distant future. 



The round conception of the history 

 shaped it as a progress from excess to 

 emaciation, a sliding down the scale; it 

 made the life history but an episode inter- 

 current in the great decline from the too 

 hot and the too much to the too cold and 

 the too little. 



The logic in all this is plausible. Start- 

 ing with the hypothetical premises, the 

 conclusions seem to follow. Variations of 

 detail might well be found in the complexi- 

 ties of the case. Especially might sources 

 of supply be assigned to offset waste and 

 loss in some degree, but granting the pre- 

 mises the conclusion is not easily escaped. 

 In point of fact the general conception 

 dominated the geologic thought of the last 

 century. Not only this, but in no small de- 

 gree it gave direction to the interpretations 

 and in some measure even influenced the 

 observations of geologic phenomena well 

 down to the close of the century and is far 

 from obsolete to-day. 



But logical and plausible as was this 

 general conception of earth-history, it was 

 hung, as you have not failed to notice, on 

 the hypothesis of the genesis of the earth 

 accepted. However logical, its logical 

 strength was only that of the hypothesis on 

 which it was hung. I say its logical 



strength advisedly, for outside the logic of 

 the general concept there was always the 

 appeal to the concrete evidences of the 

 geologic record. This appeal was made, 

 and was thought to be on the whole con- 

 firmatory. The strata of high latitudes 

 were found to contain relics of life of 

 tropical or sub-tropical types, not only in 

 the early stages but well down toward re- 

 cent times. Figs and magnolias grew in 

 Greenland as late as the Tertiary period. 

 Phenomena so striking gave deep hold to 

 the logical scheme. Phenomena not so 

 consonant with it were easily overlooked or 

 lightly passed by as is our wont when too 

 much impressed by what must be true. It 

 is, however, a merit of modern science that 

 it puts that which is to the front and that 

 which logically must he in a secondary 

 place. And so during the past century 

 inconsonant data were gathered with the 

 consonant. Most of the inconsonant facts 

 were of the unobtrusive sort, but yet some 

 of them were startling, were seemingly in- 

 credible, were indeed long doubted and 

 only slowly gained credence. The accumu- 

 lation of this inconsonant data gradually 

 weakened the hold of the general logical 

 concept and prepared the way for a recon- 

 sideration. 



Meanwhile a serious source of doubt had 

 arisen on the logical side, from the progress 

 of physics. The older hypotheses of the 

 origin of the earth had been framed before 

 the kinetic theory of gases was evolved. 

 After the kinetic view was accepted it was 

 pointed out by Johnstone Stoney that the 

 velocities of the molecules of the outer air 

 place a limit to the volumes which plane- 

 tary atmospheres may possess. When the 

 test which this suggested was applied to the 

 postulated atmospheres and voluminous 

 gaseous states of the early earth, it gave 

 rise to grave doubt as to the physical con- 

 sistency of these conceptions. 



