810 



SCIENCE. 



[N. S. Vol. IV. No. 101. 



certainly favors the inclusion of the Weal- 

 den rocks in the Jurassic series."* 



AGE OF THE LAEAMIE. 



The problem- before us to-day has a 

 strong family resemblance to another with 

 which geologists were face to face twenty 

 years ago ; namely, the geological age of 

 the great lignite series of the West. Then, 

 as now, the plants and the animal remains 

 seemed to tell a different story, and I was 

 thus led to investigate the question with 

 considerable care. It may perhaps aid in 

 solving the present problem if I repeat what 

 I then said so far as it relates to the value 

 of different kinds of fossils as evidence of 

 geological age. In an address before the 

 American Association for the Advancement 

 of Science, in 1877,t I stated the case as 

 follows : 



" The boundary line between the Creta- 

 ceous and Tertiary in the region of the 

 Eocky Mountains has been much in dispute 

 during the last few years, mainly in conse- 

 quence of the uncertain geological bearings 

 of the fossil plants found near this horizon. 

 The accompanying invertebrate fossils have 

 thrown little light on the question, which 

 is essentially whether the great Lignite 

 series of the West is uppermost Cretaceous 

 or lowest Eocene. The evidence of the 

 numerous vertebrate remains is, in my 

 judgment, decisive, and in favor of the 

 former view. 



KELATIVE IMPOKTANCE OF FOSSILS. 



" This brings up an important point in 

 paleontology, one to which my attention 

 was drawn several years since ; namely, 

 the comparative value of different groups 

 of fossils in marking geological time. In ex- 

 amining the subject with some care, I found 

 that, for this purpose, plants, as their na- 



* Catalogue British Museum, "Wealden Flora, p. 

 290, 1895. 



-\ American Journal of Science, Vol. XIV., pp. 338- 

 378, November, 1877. 



ture indicates, are most unsatisfactory wit- 

 nesses; that invertebrate animals are much 

 better ; and that vertebrates afford the 

 most reliable evidence of climatic aad 

 other geological changes. The subdivisions 

 of the latter group, moreover, and in fact 

 all forms of animal life, are of value in this 

 respect, mainly according to the perfection 

 of their organization or zoological rank. 

 Fishes, for example, are but slightly affected 

 by changes that would destroy reptiles or 

 birds, and the higher mammals succumb 

 under influences that the lower forms pass 

 through in safety. The more special appli- 

 cations of this general law, and its value 

 in geology, will readily suggest themselves." 



In the statement I have quoted I had no 

 intention of reflecting in the slightest de- 

 gree on the work of the conscientious paleo- 

 botanists who had endeavored to solve the 

 problem with the best means at their com- 

 mand. I merely meant to suggest that the 

 means then at their command were not ade- 

 quate to the solution. 



It so happened that the most renowned 

 of European botanists. Sir Joseph Hooker^ 

 was then in this country, and to him I per- 

 sonally submitted the question as to the 

 value of fossil plants as witnesses in deter- 

 mining the geological age of formations. 

 The answer he made fully confirmed the 

 conclusions I had stated in my address. 

 Quoting from that, in his annual address as 

 President of the Eoyal Society, he added 

 his own views on the same question.* His 

 words of caution should be borne in mind 

 by all who use fossil plants in determining 

 questions of geological age, and they are 

 especially applicable to the problem now 

 before us — the age of the Potomac forma- 

 tion. 



The scientific investigation of fossil plants 

 is an important branch of botany, however 

 fragmentary the specimens may be. To at- 



* Proceedings Eoyal Society of London, Vol. 

 XXVI., pp. 441, 443, 1877. 



