ANTHRACOLITHIC ROCKS OF KANSAS 145 



The dividing line between the Carboniferous and Dyas [Permian] formations 

 cannot be drawn with full certainty in every region since, especially in the Dyas, 

 the development of a local flora is nearly always the rule and decisive differences 

 do not exist in the brachiopod fauna. 



Yet an agreement seems to be gradually forming everywhere: The line 

 dividing the Carboniferous from the Rothliegende [lower Permian of Germany] is 

 generally placed between the Ottweiler and Cusel beds; only concerning the 

 determination of the age of the French equivalents of both do differences of opinion 

 still exist. 



It is everywhere easy to distinguish Schwagerina strata and the Arta [Artinsk] 

 stage where the Medlicottiada; and the oldest Arcestidce occur. If the Arta stage 

 and the Sosio limestone, is considered a transitional horizon, i. e., as Permo- 

 Carboniferous, there remains almost nothing of our formation. 



Also, where the characteristic Dyas bivalves {Pleurophoriis, Schizodus, 

 Bakewellia, Pseudomonotis) occur in masses (Kansas) there can be no doubt about 

 the dividing line. The great development of the Stegocephala, whose Carbonif- 

 erous ancestors occur sparingly, is also characteristic of the Dyas. 



On the other hand, the development of the still very widely distributed 

 brachiopods is such, that only in the lower Dyas of the Mediterranean district a 

 few new genera, and in the north only a few new species appear. To offset the 

 slow retrogression of the Carboniferous brachiopod group, as we see e. g. in 

 Kansas, there are no additions of any kind.'^ 



Professor Frecli's deduction from tlie evidence of tlie Kansas 

 pelecypods is quite different from tfiat of Dr. Girty and is important 

 to bear in mind in considering tlie age of tliese formations. Dr. Frecli 

 wrote tliat : in tlie braciiiopod formations enter layers agreeing petro- 

 graphically which contain a fauna of small Dyas bivalves {Bakewellia, 

 Pleurophorus, Schizodus). But in the two transition horizons 

 (Neosho and Chase) the Carboniferous brachiopods predominate. 

 The Marion strata are the first to be filled exclusively by upper 

 Dyas bivalves and with variegated gypsum-bearing marls devoid of 

 fossils.^ 



Dr. Girty states that "he [Prosser] finds the Kansas 'Permian' 

 fauna much more distinct from the underlying Pennsylvanian than 

 appears to me warranted, and he correlates it too confidently with 

 the Russian Permian. "^ In regard to the opinion expressed in the 

 first clause of the above sentence those who have followed this dis- 

 cussion have seen that there are other paleontologists who have 



1 Lethaea geognostica, " Lethaea paleozoica," 2. Band, 3. Lief., 1901, pp. 490, 491. 



2 Ihid., 2. Lief., 1899, p. 377. 3 Op. cit., p. 42. 



