FOSSIL PLANTS AS AN AID TO GEOLOGY. 



Paleobotany, together with all the other branches of paleon- 

 tology, admits of subdivision into two lines, or fields of study — 

 the biological and the geological — depending upon the promi- 

 nence that is given to the one or the other of these subjects. 

 The biological study concerns itself with the evolution of the 

 vegetable kingdom, that is, with the tracing of the lines of 

 descent through which the living flora has been developed. The 

 geological side of paleobotany has "^two phases, one of which 

 concerns itself with the associations, time relations, and distribu- 

 tion of the plant forms which constitute the successive floras of 

 the geological ages and form an important element in the life 

 history of the earth, while the other is concerned principally with 

 the use of fossil plants as stratigraphic marks, but also with any aid 

 that may be rendered in elucidating the many intricate problems 

 which geology presents. The latter, or geological aspect, is 

 almost exclusively the phase of the subject to which the present 

 paper is devoted. 



Before passing to an elaboration of the claims that paleo- 

 botany may have as an aid to geology, it may not be out of 

 place to call attention to the fact that the successful use of 

 fossils as stratigraphic marks is, or at least may be, entirely 

 independent of their correct biological interpretation. It makes 

 not the slightest difference to the stratigraphic geologist whether 

 the fossils upon which he most relies are named at all, so long 

 as their horizon is known and they are clearly defined and 

 capable of recognition under any and all conditions. They 

 might almost as well be referred to by number as by name, 

 although, of course, every paleontologist seeks to interpret to 

 the best of his knowledge the fossils that he studies. He 

 may, probably often does, make mistakes in his attempts to 



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