UPPER PALEOZOIC FLORAS 143 



THE CARBONIFEROUS FLORAS 

 MISSISSIPPIAN ("lower CARBONIFEROUS") 



Characters. — The step from the Upper Devonian tiora to that of 

 the Mississippian (" Lower Carboniferous ") is marked by a floral con- 

 trast which, in some regions, is unexpectedly sharp though the warping 

 of the Devonian floor to form the new Carboniferous synclines and 

 the contraction of the seas naturally premise distinct climatic as well 

 as other environmental changes. The new flora which lived in the 

 restricted basins of the early Mississippian consists of Triphyllopteris, 

 the broad, large-pinnuled Aneimites, the linear (flaccida) type of 

 Sphenopteris, Cyclostigma, Eskdalia, and the acuminate Lepido- 

 dendra chiefly of the corrugatum group. 



Lowest stage — Pocono. — The early Mississippian was a time of 

 sea expansion; and in a number of distant areas, such as the northern 

 part of the Appalachian trough, northern Alaska, the eastern Arctic, 

 Scotland, and southern Siberia, the conditions at this moment were 

 favorable for the formation of considerable coals. 



Source. — Since the vegetation was presumably most luxuriant in 

 these regions of coal formation, and since greatest evolution of forms 

 attends most rapid and luxuriant expansion of a flora, we are perhaps 

 safe in supposing that these are probably the regions of evolution of 

 the flora as a whole. 



Regional differences. — In this connection it may be noted that, 

 either on account of land or marine barriers, or because the climatic 

 conditions throughout the northern hemisphere may at the outset have 

 been less uniform than in the preceding epoch, the different areas 

 exhibit more or less distinct local floral differences. Thus in the 

 Pecono of West Virginia and Eastern Pennsylvania where Triphyl- 

 lopteris and the corrugatum type of Lepidodendron are almost without 

 competition, the former achieved a remarkable differentiation far sur- 

 passing that known in any other area. In Nova Scotia, on the other, 

 hand, the Horton series, which I regard as practically contempo- 

 raneous with the Pocono, contains the same Lepidodendra, accom- 

 panied, however, by Aneimites instead of Triphyllopteris. In both 

 these regions the formations are in close relations with the Upper 

 Devonian — in fact, probably in continuous sequence at one point or 

 another. But the Pocono flora is apparently nearer to the Arctic 



