240 ENVIRONMENT OF VERTEBRATE LIFE, ETC. 



" It may, however, be noted that in the red-bed regions coal formation usually 

 falls off in the thickness if not in the number of the beds; on the other hand, the 

 greatest coal formation of the Conemaugh occurs in general in the districts of 

 least red-bed deposition. We may therefore infer either that the conditions 

 favorable for redness in such cases involve relations of topography, water-level, 

 and epirogenic movement that are less favorable to thick and repeated fresh- 

 water peat formation or that a drier state of the land surrounding the swamp 

 not only caused a less rank growth of plant life, but also, by reducing the run-off 

 through jungles formerly tropical in density, permitted smaller burdens of nearly 

 pure vegetal matter to add to that growing in the somewhat reduced swamps. 

 It is possible that in certain regions comparative aridity prevailed for restricted 

 periods during which the floras found a not too distant friendly refuge, from which 

 they returned with the resumption of favorable conditions without too great loss 

 or changes. 



" MONONGAHELA TlME. 



"Monongahela (Upper Stephanian) time is marked in many regions of the 

 earth by conditions approaching in some respects those of the Allegheny. The 

 Appalachian, as well as the contemporary beds in western Europe, eastern Asia 

 (Manchuria and China), and southeastern Africa, are nearly everywhere marked 

 by heavy deposition of coal. 



"Among the notable paleobotanical characters of this stage are (a) the 

 presence of a waning group of thick-barked Sigillariae, probably confined abso- 

 lutely to swamps; (b) large and abundant Psaronius tree ferns; (c) increasing 

 size of Calamites, reinforced by increased wood development; (d) high differentia- 

 tion of types of seeds, that is, expansion and differentiation of the seed-bearing 

 habit, as the great spore-bearing types were eliminated, probably in consequence 

 of occasional seasons of unusual dryness; (e) increase of features, possibly xero- 

 phyllous, especially in the surviving and new cycadofilices, including Noeggerathia 

 and Dolerophyllum, though most of these are presumably exclusively swamp 

 plants; (/) first appearance of fronds of distinctly cycadaceous aspect (Ptero- 

 phyllum, Sphenozamites, Plagiozamites) . The nearest living relatives of these, 

 as well as of the tree ferns, are tropical or subtropical, and though many of them 

 are accustomed to survive dry seasons, they are characteristic evidence against 

 winter frost. Testimony against winter cold and prolonged seasons of drought, 

 such as would ordinarily prevent peat (coal) formation, especially in a warm 

 climate, is also found in the stage of development of seasonal rings in the wood, 

 the latter being usually slight and sometimes very indistinct, thus showing that 

 the period of interruption or retardation of growth was usually of short duration. 

 Both the survival of warm-climate types and the evidence for relatively short 

 periods unfavorable to growth argue against winter seasons of frost during this time. 



"On the whole, the paleobotanical inferences are that during Monongahela 

 time the climate was mild, probably subtropical, and nearly uniform over the 

 greater part of the earth, as shown by the geographic distribution of the types 

 that were able to extend in relative purity of association of identical species 1 

 around the world from east to west, and from the latitude of England and Man- 



1 Seven of the eight species described by M. Zalessky (Verh. Russ. K. Min. Ges., vol. 42, 

 i9O5i PP- 485-508) from the mines at Jantai in Manchuria are also present in western 

 Europe, six of them being present in America also. All of the eleven species reported 

 by R. Zeiller (Ann. des Mines, vol. 4, 1883, pp. 594-598) from Tete on the Zambesi are 

 present in Europe, and nine or ten of them are also found in the Appalachian trough. 



