UPPER PALEOZOIC FLORAS 159 



Coal- formation in Permian. — The lower Permian of Germany, 

 France, Russia, and Pennsylvania, is commercially coal-bearing, 

 while the Permian red beds of Kansas and Texas carry thin coals. 

 Professor C. A. Davis informs me that in the United States today 

 the formation of peat, the first stage of coal, is practically confined 

 to the zone having twenty inches, or more, of rainfall. 



Flora in red beds not perceptibly different from that in other sedi- 

 ments. — The plants in the Monongahela and Conemaugh do not seem 

 to dift'er in kind whether the series are gray and limestone-bearing 

 in Pennsylvania, or red and nearly devoid of limestones seventy-five 

 miles to the south in West Virginia; except that although sometimes 

 fairly abundant, they are very difficult to find in the red shales because 

 the carbon of the plants is almost or entirely gone, as the result of 

 destructive decomposition, only impressions of the leaves being left. 

 Is it not possible that, in some instances, the causes of red-bed deposi- 

 tion lie to a large extent in relatively slow subsidence of the basin, and 

 in differential warping to permit exposure, with some redeposition 

 and dehydration ? It is probable that there was aridity in certain 

 regions and during certain intervals of the Permian; but there was 

 evidently enough moisture to produce most extensive glaciation, and, 

 later, to promote the formation of coals over broad areas in the 

 great fresh-water Gondwana series laid down on the continents of 

 South America, Africa, and Asia. The beds with the Gangamopteris 

 flora are in most regions coal-bearing, usually commercially. 



Date oj glacial episode.- — If one looks for climatic fissures, or dis- 

 locations into which to fit the relatively brief episode of Gondwana 

 glaciation it is difficult either in western Europe, or in America, to 

 find an opening between the base of the Westphalian and the top of 

 the Lower Permian in which it may be fixed. It is true that, in most 

 sections, we have intervals in which no plants are found; and, further, 

 the lesson of Pleistocene deposition shows what sweeping climatic 

 changes may occur and recur within a relatively insignificant thickness 

 of strata. Yet, while the gap is often large enough in stratigraphical 

 view, the plant-sequence so tightly closes it as to preclude a possible very 

 distant exile of the flora for a time. We may therefore conclude that 

 the glacial episodes probably occurred at the time of one of the oro- 

 genic movements; and, if so, preferably at one marked by the most 



