542 GEOLOGY. 



on the conditions he furnishes. But even the accelerated evolution 

 of these organisms is a part of the profound biological revolution which 

 attends man's dominance. 



Man's control has not thus far been characterized by much recog- 

 nition of the complicated interrelations of organisms and of the con- 

 sequences of disturbing the balance in the organic kingdom, and he 

 is reaping, and is certain to reap more abundantly, the unfortunate 

 fruits of ignorant and careless action. For the greater part man 

 has been guided by immediate considerations, and even these not 

 always controlled by much intelligence, while great wantonness has 

 attended his destruction of both plant and animal life. But a more 

 intelligent as well as a more sympathetic attitude is developing, and 

 will doubtless soon become dominant. 



A new era in control and in evolutionary selection is dawning. 

 New varieties and races are being produced that not only depart widely 

 from the parent stock, but diverge in lines chosen to meet given con- 

 ditions, or to produce desired products. How far this may yet go 

 it is impossible now to predict. But it may be worth while to suggest 

 that some of the species man is wantonly destroying may possess capa- 

 bilities of mutation quite beyond present apprehension, and that no 

 species should be allowed to pass utterly beyond reach forever until 

 man shall learn more about its ulterior possibilities. 



Prognostic Geology. — The long perspective of the past should 

 afford at least some suggestions of the future, but it must be con- 

 fessed that the most important previsions are dependent on inter- 

 pretations of the past that have not yet emerged from the tentative 

 state. A word has been said relative to a possible return of a glacial 

 epoch, but this is contingent on agencies that are yet matters of hypoth- 

 esis, and no sure prediction can be offered. Question has been raised 

 as to whether the end of the recent period of deformation has come 

 and a gradation into another period of quiescence and equable genial 

 conditions has begun ; but the answer hangs on the doctrine of periodicity 

 of deformation and quiescence which does not yet command universal 

 assent, and if it were given, there would remain the further question 

 whether the period of deformation is completed. The duration of the 

 earth as a habitable globe lias been a common theme of prognosis. 

 A final refrigeration as the result of the secular cooling of a once molten 

 globe has been the usual forecast, and the final doom of the race has 



