288 ANNUAL BEPORT SMITHSONIAN INSTITUTION, 1925 



smaller cycles; and that, on account of their interference with, or 

 reinforcement of. one another, the simpler type of cyclic repetition 

 which mijiht have heen looked for in the history is masked and 

 broken and diversified by actual happenings of an infinite variety. 



Van Hise more than once comi)lained of the tendency of <,feologists 

 to adhere to single explanations of events, and advocated the neces- 

 sity of considering the cooperation of many causes; and it may well 

 be that in many outstanding pi'ol)lems such as past glacial or tro])i- 

 cal periods, coral reefs, stages of earth movement, progression and 

 regression of the oceans, we may find the ultimatxi explanation in the 

 interaction of a number of " true causes." 



EVOLUTION 



During the long period of time comprised in the history from the 

 Cambrian ])eriod onwards, the slow and persistent evolution of 

 plant and animal life Avent forward and left ample record in the 

 rocks. To warrant a belief in organic evolution, we are no longer 

 solely dependent on reasoning founded on existing organisms or on 

 the facts of their ontogeny and distribution. As M. Marcellin Boule 

 says in his work on Fossil Man, " * * * pour tout ce qui a trait 

 a revolution des etres organises en general, le dernier mot doit rester 

 a la Paleontologie quand cctte science est en measure de parler claire- 

 ment. Les plus fins travaux anatomiques, les comparaisons les plus 

 approfondies, les raisonnements les plus ingenieux sur la morpholo- 

 gic des etres actuels ne sauraient avoir la valeur demonstrative des 

 documents tires de la roche ou ils sont enfouis et disposes dans leur 

 ordre chronologiquc meme."*- Although we are only too painfully 

 aware of the innumerable chances tlial conspire to prevent an animal 

 or plant from securing immoi-tality by preservatictn as a fossil, the 

 finding of better preserved material, the more skillful ])ieparation 

 of it for examination, and the application to it of refined biological 

 methods, such as careful dissecti(*n and (he serial sections of Profes- 

 sor Sollas, are giving us more comi)lete and accurate knowledge than 

 ever before. It may now be confidently stated that many of the 

 most crucial links in the chain of e\<)l\ing life are in oiii- hands; 

 that they actually lived in the past, and tluit their fossil forms show 

 their rehvtionship to their predecessors and successors. The time has 

 come when Darwin's famous chapter on the *' Imi)erfection of the 

 Geological Record,'" an ai)()logy am-jUcu with the most balanced 

 criticism and unbiased judgment, should be rewritten and revised. 



It is true that we seem as far as evei- fioni unNciling the points of 

 divergence of the gi-eat phyla, and we can but I'eel that the time from 

 the beginning of the Cambrian period onward is l)ut a small part of 



* Marcelliii Boule, Les Homnies Fossiles, li>23, p. 45;^. 



