484 0. C. Marsh — Comparative Value of Different 



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 forma- 

 tions. The answer he made fully confirmed the conclusions I 

 had stated in my address. Quoting from that, in his next 

 annual address as president of the lloyal 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 deter- 

 mining 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 labor 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 instruction 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 recognize 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 geologi- 

 cal 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 specialization. In the Inverte- 

 brates, .for instance, 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 formations, however, shows little advance. Even the 

 recent forms of the same group have no distinctive characters 

 sufficiently important to mark geological horizons. 



* Proceedings Royal Society of London, vol. xxvi, pp. 44-1-443, 1877. 



