GEOGRAPHICAL DISTRIBUTION. 



51 



Eastern America during the long interval of elevation and ero- 

 sion, which occupied all of Jurassic time, offers many potential 

 possibilities as a theater of evolution, as it undoubtedly was, but 

 the simultaneous appearance of identical types in the mid-Creta- 

 ceous of Europe and America and Greenland is hard to under- 

 stand if either America or Asia was the center of dispersal. The 

 remaining alternative is that of regarding the Arctic area as the 

 scene of evolution and center of dispersal of the modern flora, 

 and, possibly, the fauna as well. The facts, while suggestive, 

 are insufficient for definite conclusions. They serve to explain, 

 for instance, the presence of the oldest known Coniptonia in 

 deposits in Greenland, New Jersey, Sweden and Bohemia, which 

 are probably all of Cenomanian age; the presence of Moriconia 

 from Greenland southward to South Carolina on this continent 

 and in central Europe at the same time. In fact, numberless 

 parallels could be drawn between the Albian and Cenomanian 

 of America and Europe, so that at least tentatively we may pic- 

 ture successive waves of plant migration sweeping southward 

 from the Arctic region somewhat as indicated by tlie arrows in 

 Figure 3, the recorded floras of middle and later Cretaceous age 

 beinsf indicated bv the solid black areas. 



Fig. S- — Sketch map of the world, showing approximate location of mid- 

 Cretaceous plant-bearing deposits (in black). Arrows indicate possible direc- 

 tions of migration. 



