870 REPORT— 1S98. 



uppermost Cretaceous or lowest Eocene. The evidence of the numerous vertebrate 

 remaius is, in my judgment, decisive, and in favour of the former view. 



' This brings up an important point in palaeontology, one to which my attention 

 was drawn several years since — namely, the comparative value of different groups 

 of fossils in marking geological time. In examining the subject with some care, I 

 found that, for this purpose, plants, as their nature indicates, are unsatisfactory 

 witnesses ; that invertebrate animals are much better ; and that vertebrates afford 

 the most reliable evidence of climatic and other geological changes. The sub- 

 divisions of the latter group, moreover, and in fact all forms of animal life, are of 

 value in tliis respect, mainly according to the perfection of their organisation or 

 zoological rank. Fishes, for e.xample, are but slightly affected by changes that 

 vrould destroy reptiles or birds, and the higher mammals succumb imder influences 

 that the lower forms pass through in safety. The more special applications 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 

 degree on the work of the conscientious palfEobotanists -who had endeavoured to 

 solve the problem with the best means at their command. I merely meant to 

 suggest that the means then at tbeir command were not adequate to the solution. 



It so happened that one of the most renowned of European botanists. Sir 

 Joseph Hooker, was then in America, and to him I personally submitted the 

 question as to the value of fossil plants as witnesses in determining the geological 

 age of formations. The answer he made fully confirmed the conclusions I had 

 stated in my address. Quoting from that, in his ne.tt annual address as President 

 of the Royal Society, he added his own views on the same question.' His words 

 of caution should he. borne in mind by all who use fossil plants in determining 

 questions of geological age. 



The scientific investigation of fossil plants is an important branch of botany, 

 however fragmentary the specimens may be. To attempt to make out the age of 

 formations by the use of such material alone is too often labour lost, and must 

 necessarily be so. As a faithful pupil of Goeppert, one of the fathers of fossil 

 botany, I may perhaps be allowed to say this, especially as it was from his instruc- 

 tion that I first learned to doubt the value of fossil plants as indices of the past 

 history of the world. Such specimens may indeed aid in marking the continuity 

 of a particular stratum or horizon, but without the reinforcement of higher forms 

 of life can do little to determine the age. 



The evidence of detached fossil leaves and other fragments of foliage that may 

 have been carried hundreds of miles by wind or stream, or swept down to the 

 sea-level from the lofty mountains where they grew, should have but little weight 

 in determining the age of the special strata in which they are imbedded, and 

 failure to recognise this fact has led to many erroneous opinions in regard to 

 geological time. There are, however, fossil plants that are more reliable witnesses 

 as to the period in which they lived. Those found on the spot where they grew, 

 with their most characteristic parts preserved, may furnish important evidence as 

 to their own nature and geological age. Characteristic examples are found among 

 the plants of the Coal Measures, in the Cycads of Mesozoic strata, and in the fossil 

 forests of Tertiary and more recent deposits. 



The value of all fossils as evidence of geological age depends mainly upon their 

 degree of specialisation. In the invertebrates, for example, a Linguloid shell 

 from the Cambrian has reached a definite point of development from some 

 earlier ancestor. One from the Silurian or the Devonian, or even later forma- 

 tions, however, shows little advance. Even the recent forms of the same group 

 have no distinctive characters sufliciently important to mark geological horizons. 



If we take the Ammonites as another example from the Mollusca the case is 

 totally different. From the earliest appearance of this family the members have 

 been constantly changing, developing new genera and species, each admirably 

 adapted to mark definite zones or horizons, and already used extensively for that 

 purpose. 



' Froc. Roy. Soc. Loud., vol. sxvi. pp. 441, 143, 1877. 



