530 F. H. KNOWLTON FOSSIL PLANTS IN GEOLOGIC CORRELATION 



the greatest value in indicating the age correlation of a horizon of previ- 

 ously unknown or uncertain position. The discovery of such a guide 

 fossil immediately suggests lines of search for additional corroborative 

 data. 



It need hardly be pointed out that the presence of a single specimen, 

 perhaps only a mere fragment, may be relied on to indicate the larger 

 units in the time scale. Thus the finding of Lepidodendron or Sigillaria 

 indicates that the beds containing them are older than Mesozoic, the 

 presence of a dicotyledon that the beds are Cretaceous or younger, or the 

 finding of a Dictyophyllum that the age is older Mesozoic, etcetera. 



It is perhaps also unnecessary to call attention to the fact that the study 

 of fossil plants — or all fossils for that matter — should not be permitted 

 to foster neglect in securing all possible stratigraphic aid, for, as Ulrich 

 has well said, "Systematic paleontology without a stratigraphic basis is 

 regarded as an absurdity." Each complements and supplements the other, 

 and when the story is read aright there will be found to be no conflicts or 

 essential disagreements. 



In conclusion, the writer may perhaps be pardoned a moment of retro- 

 spect over the accomplishments of paleobotany during the last quarter 

 of a century. At the beginning of that period the study of fossil plants 

 had small part in the councils of stratigraphic geology, but since that 

 time, thanks to a small but earnest body of workers in all parts of the 

 world, it has come to be a recognized and, it is believed, a respected inte- 

 gral part of the greater science of stratigraphic paleontology. It is not 

 claimed that it is the golden^ key fhat is to unlock all the mysteries of 

 geologic history — nor for that matter is any of the other of the 57 varie- 

 ties into which the vast subject is now divided — but, within its proper 

 and legitimate limit, it is believed to have won for itself a "Place in the 

 Sun 1" 



