UPPER CARBONIFEROUS 127 



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 hmestone 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, 

 cjuite 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 

 Upper Carboniferous faunas of the continental basin do not show 

 differentiation during this long interval, for the Pottsville group has 

 a distinct fauna and appreciable changes occur in the later Pennsyl- 

 vanian. But the changes are by no means so marked as one would be 

 led to expect from the thickness of the strata involved, the extent of 



