308 GEORGE H. GIRTY 
coals, which toward the East play so important a part, if not in thick- 
ness at least economically and significantly in the Carboniferous 
sediments, are there practically absent. From this it has been justly 
inferred that the character of the eastern Carboniferous indicates 
shore and estuarine conditions of deposition, while that of the western 
indicates marine conditions of deposition. ‘There are, however, vast 
amounts of sandstone and shale in the Upper Carboniferous of the 
West. 
It seems to be true that the greatest deposits of limestone in this 
series are found rather to the Southwest than to the West and the most 
notable thicknesses of sandstone and conglomerate rather to the 
Northeast than to the East. 
There is one other phenomenon of more than local interest which 
should not be omitted in a commentary on the lithologic features of the 
Upper Carboniferous. I refer to the red beds of the West and South- 
west. The age, the stratigraphic relations, the sources, and the cause 
of the peculiar coloration of this great series of sandstones and con- 
glomerates form a problem of no mean difficulty and importance. 
Although it is difficult to trace these beds stratigraphically, and though 
fossils are rarely found in them, we know now that sediments of this 
character were formed rather early in the Pennsylvania and succes- 
sive manifestations recurred at various periods on into the post- 
Cretaceous. ‘That there were continuous red beds conditions during 
all this period seems out of the question, and also that red beds con- 
ditions repeatedly recurred. Some‘of the occurrences can probably 
be best explained as a reworking of older materials under conditions 
unlike those which determined their original character. 
In considering the faunas of the later Paleozoic—those of the 
Pennsylvanian and Permian—several facts of a general nature can be 
stated. ‘The Upper Carboniferous faunas of western North America 
have a facies markedly different from those of the eastern part and 
are closely comparable to the corresponding faunas of Asia and 
eastern Europe. A second fact of general import seems to be that, 
quite in contrast to the unstable physical conditions in which they 
lived, these eastern faunas, which range, let us say, westward to the 
Rocky Mountains, are remarkably uniform both in their geographic 
distribution and in their range. I would be far from saying that the 
