1 88 THE JOURNAL OF GEOLOGY. 



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 local- 

 ities difificult, 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. 



COMPARISON WITH THE PERMO-CARBONIFEROUS OF KANSAS AND 



NEBRASKA. 



The fauna of the Upper Coal Measures of Arkansas has a 

 strong resemblance to that of youngest Paleozoic beds of Kan- 

 sas and Nebraska, described as Permian by Professor Geinitz.^ 



F. B. Meek redescribes this fauna,^ and comes to the conclu- 

 sion that the rocks in question are not to be referred to the Per- 



' " Carbonformation und Dyas in Nebraska." 



^ Final report U. S. Geol. Survey of Nebraska, etc., pp. 128 et seq. 



