Page:The Journal of geology (IA journalofgeology21894univers).pdf/381

Paleobotany, together with all the other branches of paleontology, admits of subdivision into two lines, or fields of study—the biological and the geological—depending upon the prominence 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 distribution 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 paleobotany 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