Page:The Journal of geology (IA journalofgeology21894univers).pdf/202

give a total of 48 genera and 78 species, 31 species in the Lower Coal Measures, and 51 in the Upper, with 4 species common to both.

It is not thought that this small number of species represents the entire fauna, or that only four species are common to the two divisions, for the collections were much too scattered and too meager to exhaust the possibilities.

But the fauna is a poor one, such as one would expect to wander in from deeper waters, whenever a slight subsidence had made the shallow water a little more habitable. The fauna could not become well established, because the conditions soon reverted to their old state, and the inhabitants of the seas were forced to migrate or were exterminated.

There is, therefore, no gradual transition here from the fauna of the Lower Carboniferous limestone, since the presence of these fossils depends on the transgression of the sea on land areas, and the fossils of the Lower Coal Measures are just as different from those of the Lower Carboniferous as are those of the Upper Coal Measures.

No successful division of the Coal Measures into zones has ever been carried out, and in the present state of our knowledge it cannot be done. This makes the correlation of distant localities difficult, since the vertical range of species in the Coal Measures is very little known. Therefore, the range of the species in Arkansas cannot be given any closer than the two great divisions of the Coal Measures.

The fauna of the Upper Coal Measures of Arkansas has a strong resemblance to that of youngest Paleozoic beds of Kansas and Nebraska, described as Permian by Professor Geinitz.^[1]

F. B. Meek redescribes this fauna,^[2] and comes to the conclusion that the rocks in question are not to be referred to the Per-