340 DAVID WHITE 
Coal-jormation 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 jrom that in other sedi- 
ments.—The plants in the Monongahela and Conemaugh do not seem 
to differ 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 
