TROPIDOLEPTTJS FAUNA IN MARYLAND CHEMUNG 685 



to be very hazardous to attempt a correlation of the conglomerates over a 

 large area by their position in the section without faunal evidence, which has 

 not yet been secured. 



Correlation with the Upper Devonian of New York 



The comparison of the sequence of the Upper Devonian strata in Maryland, 

 as shown by the above sections, and that in New York, recorded by Williams, 10 

 shows a striking similarity. 



Section in Maryland Section at Ithaca, New York 



Sandstones and shales 



Upper conglomerate, 25-50 Fall Creek conglomerate, 0-10 



Sandstone and shales, 700-800 Wellsburg sandstone, 600-650 



Upper Tropidoleptus carinatus Zone Tropidoleptus carinatus Zone 



Shales and sandstone, 500-700 Cayuga shale, 600 



Lower Tropidoleptus carinatus Zone Enfield shale (with recurrent Tropido- 



(Spirifer mesacostalis Zone), 300-600 leptus fauna), 550-800 



Shales and sandstone, Ithaca fauna Ithaca shale 



Shales and sandstone with Naples fauna Sherburne flagstone with Naples fauna 



Genesee, absent in east Genesee 



The sequence of the faunas is the same, both in New York and in Maryland, 

 while there is a marked similarity in the lithological features. The close simi- 

 larity of the sections, both lithologically and faunally, is striking and indicates 

 that the Upper Devonian of Maryland and New York were laid down in a 

 common basin and under similar conditions. 



Geographical Range of the Genera Dalmanella and Douvillina in 



Maryland 



In examining the distribution of the species of the Chemung fauna certain 

 features are to be noted. Species of the genus Dalmanella are very rare east 

 of the Wills Mountain anticline. Up to this time the author and his associates 

 have not observed a single specimen of Dalmanella east of Wills mountain, 

 and but a single valve has been reported from that region by others. West of 

 Wills mountain, on the contrary, they are abundant. Again, species of Dou- 

 villina are not common east of the same locality, while they are very abundant 

 west of it. Spirifer disjunct us, however, is abundant throughout the area. 



A somewhat comparable condition seems to exist in New York, where Wil- 

 liams" does not cite any species of Dalmanella from the eastern part of the 

 state in his recent paper on the genus Dalmanella. The reason for these facts 

 is not clear. Wills mountain is the high western arch of the Alleghany moun- 

 tains. The marked difference in the fauna east and west of it suggests the 

 possibility that the arch may have begun to rise early in Upper Devonian time, 

 forming a submerged barrier at that time. This is a mere suggestion, how- 

 ever, and needs further confirmation before being worthy of acceptance. 



The facts given may be summarized in the following conclusions : 



10 Williams : Devonian section of Ithaca, N. Y. Journal of Geology, vil. xiv, p. 579. 

 n Proceedings of the U. S. National Museum, vol. xxxiv, 1908. 



