178 EVOLUTION AND DOGMA. 



and mathematicians can agree among themselves, as 

 to the data on which they base their calculations, and 

 until they can furnish more satisfactory results than 

 they have hitherto offered, geologists will be quite 

 within their right in regarding the objections urged 

 as negative or indifferent, 



In all discussions relating to the ascent of life and 

 the paucity of transitional forms, we should not lose 

 sight of the fact that ours is a period of tranquility, 

 and that, therefore, in accordance with the principles 

 of Evolution, there should now be fewer changes in 

 the fauna and flora of the earth than during periods 

 of change and widely-extended disturbance. But 

 the earth has not always been so stable and tranquil. 

 During the inconceivably long interval which has 

 elapsed since the first beginnings of life on our globe, 

 there have been countless periods of equilibrium 

 alternating with changes which were more or less 

 paroxysmal. The last of these critical epochs was 

 during that long stretch of time, known as the Gla- 

 cial Period, when ice and snow reigned supreme over 

 a great portion of Europe and North America. And 

 during these long geologic rhythms, these alterna- 

 tions of upheaval and subsidence, of denudation and 

 sedimentation, during these periods of comparative 

 tranquility and almost cataclysmal mutation, there 

 were alternately periods which in the one case fa- 

 vored the permanence of species, and in the other 

 were conducive to their rapid metamorphosis, and to 

 the speedy production of intercalary forms which 

 connected all the links of living organisms in one 

 grand unbroken chain. 



