PALEOBOTANY BERRY. 401 



THE TERTIARY FLORAS. 



The classic chronologic subdivisions of the Tertiary are, from oldest 

 to youngest : Eocene, Oligocene, Miocene, and Pliocene. These were 

 based in the first instance largely on the percentage of living species 

 of Mollusca in the rocks of the Paris basin, but subsequently received 

 a lithologic and diastrophic basis. In some respects the Tertiary 

 floras are more interesting than those that preceded them, since clim- 

 ates were genial, land surfaces ample, and the vegetation was exceed- 

 ingly luxuriant and varied. Moreover, the key to the understanding 

 of present-day geographical distribution is largely dependent on an 

 understanding of these Tertiary floras. 



Tertiary plant remains are exceedingly abundant and include those 

 found in travertine, such as the rich Paleocene floras of Sezanne in 

 France, those entombed in amber, especially the wonderfully pre- 

 served flowers in the lower Oligocene Baltic Amber. Buried swamp 

 deposits preserved as lignite coals and the associated clays and shales 

 are rich in plants, and such deposits are common throughout the 

 world and have been particularly exploited in Europe and the west- 

 ern United States. Flood plain deposits with riverside plant types 

 abound at certain horizons, and old lake beds yield a plentiful harvest. 

 Two of the most celebrated lake deposits are those of the Miocene Lake 

 of Oeningen on the Swiss border of Baden, made classic by Heer's 

 researches, and the small Miocene lake of Florissant in the heart of 

 the Colorado Rockies, where successive showers of volcanic ash en- 

 tombed an extensive flora in the resulting fine-grained shales. Ter- 

 tiary plants are also abundant in the far north in Alaska, Ellesmere 

 Land, Greenland, Spitzbergen, and elsewhere, and they have also been 

 found on Seymour Island on the margin of the Antarctic continent. 

 Materials for the complete elucidation of Tertiary floral history are 

 being rapidly accumulated, but only a few of the more striking inci- 

 dents in this history can be mentioned in the compass of the present 

 brief review. 



An interval of emergence and land extension nearly everywhere 

 intervened between the Upper Cretaceous and Tertiary sedimentation, 

 in consequence of which and the time interval represented we find 

 that the earliest Tertiary floras show marked contrast to the Cre- 

 taceous floras that had preceded them. In middle latitudes like 

 that of the United States we find an extensive forest of hardwood 

 trees, covering not only the east, but also the great prairie region of the 

 West, since at that time there were no mountain ranges to shut off 

 the moisture-laden winds from the Pacific. Abundance of moisture 

 and luxuriance of vegetation are indicated by the abundant and ex- 

 tensive coal beds of early Tertiary age found in so many of the trans- 



