GENERAL CONSIDERATIONS AS TO EARLY CARBONIFEROUS FLORA. 303 



apparently indicate an almost incredible uniformity in climate over the 

 northern hemisphere during that period, but to necessitate also the as- 

 sumption of such intercontinental relations and conditions as to furnish 

 wonderful facilities for the exceedingly rapid, almost simultaneous, dis- 

 tribution of the genera and species. The writer is disposed to believe 

 that the conditions favorable to plant distribution and comparatively 

 uniform dispersion over the greater part of the Arctic hemisphere during 

 the period extending from the later Culm to near the middle of the Me- 

 socarboniferous have never been equaled since. That there was plant 

 migration cannot for a moment be questioned ; yet, viewed from a broad 

 standpoint, the evidence of the horizontal distribution, of the vertical 

 range, of characteristic associations (such as are to be found in the Va- 

 lenciennes and Missouri coalfields) in the different zones, and of the 

 comparatively regular succession of the floras bespeaks for the terrestrial 

 plant species of that period such climatic conditions and such facilities 

 for rapid intermigration* as to justify us in regarding the remarkably 

 similar association of identical genera and identical or closely allied 

 species which characterizes a group, zone, or, not infrequently, stage of 

 the various basins of that epoch as essentially or approximately contem- 

 poraneous in all those basins. 



It has been the custom in this country to regard the well known flora 

 of Mazon creek as representative of the plant life in existence in the 

 earliest Lower Coal Measures time, there being but little difference be- 

 tween it and the plants of the bituminous Brookville and Clarion coals, 

 the lower of which is probably fully as old as the " Buck Mountain vein," 

 the conventional baseline of the Coal Measures in the Southern and 

 Middle Anthracite fields. On the other hand, certain European paleo- 

 botanists have suggested that the flora of Mazon creek really represents 

 a stage much higher than the lowest terranes above the " Millstone Grit." 



An examination of the distribution of the species will show, if we admit 

 the syn chronologic value of the floras, that the plants of the Upper Kit- 

 tanning coal of the bituminous series or of the E vein of the Northern 

 Anthracite field, fall within and are probably contemporaneous with 

 some portion of the Geislautern beds, or the upper beds of the Westpha- 

 lian {Saarbrucker Schichten), while the flora of the G vein of the same 

 anthracite field is clearly referable to the Stephanian (Ottiveiler Schichten), 

 as appears also to be the imperfectly known flora of the Pittsburg coal.f 



In those regions of Missouri, Illinois, Indiana, Ohio, and western Penn- 

 sylvania in which the plants from the lowest coals have been studied, 



* Possibly over a minimum distance under the favoring advantage of a polychthanous develop- 

 ment of certain types. 



t The flora of the Freeport coals is so nearly unknown that its relations to those of other stages 

 or the Anthracite series is still quite uncertain. 



XI/V— Bull. Geol. Soc. Am., Vol. 8, 1896 



