398 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1918. 



the Fuson flora of the Black Hills, and over 35 per cent of the 

 Albian flora of Portugal. It would be interesting to pursue the 

 subject in more detail, to discuss the place and manner of origin 

 of this latest and most highly organized plant phylum, as well as 

 its early paths of migration, but the subject is highly speculative 

 and may well await an increase of knowledge. 



The same statement is in a measure true of attempts to describe 

 Lower Cretaceous climatic conditions. The floras are so different 

 from those of the present that any quantitative estimates are out 

 of the question. These floras do, however, show such slight changes, 

 which may be legitimately related to temperature conditions as they 

 are traced from place to place, that a marked uniformity of temper- 

 ature over many degrees of latitude must be admitted. From Peru, 

 within 15 ° of the Equator to western Greenland in latitude 70 °, 

 or Spitzbergen in latitude 78 °, the fossil plants indicate uniformity 

 of temperature. It seems obvious from a consideration of the large 

 fronded ferns and Cycadophytes that they could not have with- 

 stood a winter such as characterizes the cooler parts of the Temper- 

 ate Zone at present, nor are deciduous forms known except Laricop- 

 sis and possibly Zamites. 



THE UPPER CRETACEOUS FLORAS. 



The Upper Cretaceous was a time of surpassing interest for 

 students of floral history. Most of the survivors from the older 

 Mesozoic that characterized even the later Lower Cretaceous were 

 entirely absent or very much reduced in relative importance, while 

 dicotyledonous leaves and palms appeared at that time in large 

 numbers and great variety. The ancestry of a majority of our 

 present forest trees can be traced back to the Upper Cretaceous, 

 at which time their distribution and associates were very different. 

 Upper Cretaceous plants are much alike wherever found and the} 7 

 are known from all of the continental land masses. Very many dif- 

 ferent species have been described, especially from North America, 

 where they have been studied much more thoroughly than else- 

 where. 



Some of the largest and most interesting of the Upper Cretaceous 

 floras are those of the Dakota sandstone — a littoral sand recording 

 the transgression of a Cretaceous sea northward across the western 

 interior of North America from Texas to the Arctic Ocean. The 

 Dakota flora, described chiefly from Kansas and Nebraska, com- 

 prised several hundred species. It includes but a few Conifers — 

 mainly forms of Sequoia ; large numbers of ancestral hardwoods 

 such as the earliest known birches (Betulites), many persimmons 

 (Diospyros), beeches (Fagus), numerous figs (Ficus), Magnolias, 

 Holly (Ilex), walnut (Juglans), tulip tree (Liriodendron), cassa- 



