DISTRIBUTION OF MESOCARBONIFliROUS FLORAS. 305 



GENERAL CONSIDERATIOXS. 



General comparisons, such as those summarized in the preceding pages, 

 of the flora in hand from Missouri with the floras of the Mesocarboniferous 

 series in the principal basins of Europe show (1) so large a number of 

 identical species, (2) so great a proportion of related species, (3) so impor- 

 tant a predominance of the same floral elements, and (4) so close a general 

 parallelism in the appearance and disappearance of the types as shown m 

 their vertical distribution and occurrence in the upper beds of the- West- 

 phalian (Houiller Moyen, Saarhrucker SchicJden), that the conclusion that 

 the lower coals of Henry County, Missouri, were deposited near the close 

 of that period is not on any demonstrable grounds avoidable. The evi- 

 dence of uniformity in the climate prevailing over Europe, within the 

 Arctic Circle,^ in North America, Asia, and, to some extent at least, in the. 

 southern hemisphere, during early Carboniferous time, is too generally 

 recognized to require discussion as to the fact. The astonishingly large 

 proportion, not only of genera, but of species as well, found to be identical 

 in the Culm and Mesocarboniferous in all the basins of Europe, North 

 America, and China, and the comparative regularity in the sequence of the 

 floras in these basins, are so strongly marked as to leave little room for doubt 

 as to the extremely intimate connection of the floras living about the respec- 

 tive basins, or the existence of continental conditions necessary to then- 

 rapid, almost simultaneous and uniform, distribution. The extremely close 

 relationship, so well known to paleobotanists, between the respective floras 

 of the Culm, Millstone grit (Pottsville series), and basal portions of the 

 Lower Coal Measm-es in the fields df Europe and America necessitates the 

 assumption of wonderful facihties for plant distribution during Culm and 

 early Mesocarboniferous time, facihties which, with the aid of an even climate 

 and presumably relatively low topography, made possible the comparatively 

 regular distribution and sequential order of probably nineteen-twentieths 

 of the genera and an unknown proportion (perhaps over one-half between 

 North America and Europe) of the identical species. The degree of iden- 

 tity in the types is not less remarkable than the geographic range of 



' The plants of Bear Island and Spitzbergen are shown by Nathorst not only to have inclnded 

 the common genera, but lar-elv identical species, while the individuals are as fully developed aud 

 robust as those found in the contemporaneous beds of southern Europe or the Tnited States. (See 

 Zur Paliiozoischen Flora d. Arkt. Zone, Stockholm, 1893.) 

 MON XXXVII 20 



