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But their known fauna and flora have been too limited and too indecisive to enable us to correlate subdivisions with those of other Carboniferous areas, since collections have been made in but few places, and these chiefly in sandstones, where the preservation of fossils is usually unsatisfactory, and their determination uncertain.

But the Lower Coal Measures correspond in a general way to the Strawn and the Canyon divisions of Texas, the Pottsville conglomerate series, the Lower Productive Coal Measures, and part of the Lower Barren Coal Measures of Pennsylvania.

The Upper Coal Measures.—The Arkansas Upper Coal Measures correspond to the lower part of the Cisco of Texas, and belong just at the top of the true Carboniferous, and below the transitional Permo-Carboniferous or Artinsk stage, to which latter age the uppermost Cisco beds of Texas, with Ammonites (Popanoceras) parkeri^[1] Heilprin belong. These may be the equivalents of the Poteau mountain marine beds.

The lower Permo-Carboniferous strata of Kansas and Nebraska are probably also to be correlated with the Artinsk^[2] stage, although Waagen^[3] classes the entire series with the ammonite-bearing beds of northern Texas, described by Dr. C. A. White in Bulletin 77 of the U. S. Geological Survey. The latter Texas beds, however, belong above the Artinsk stage, and in the true Permian, and are probably of the same age as the middle division of the Middle Productus limestone of the Salt Range.

Waagen, ín "Salt Range Fossils, Geological Results," p. 238, gives a comparative table, showing the relationship of the upper Paleozoic strata all over the world. While the position assigned some of the American deposits does not agree with that accepted by most American geologists, still the table is useful for comparison, and it has been freely used in compiling the comparative table at the end of this paper.