REPORT OF THE STATE PALEONTOLOGIST 1901 565 



tion of their invaluable aid in exactly correlating parts of the 

 Siluric system regionally widely separated. In the case of 

 the Tetragraptus fauna, the precise determination of its posi- 

 tion in the Beekmantown formation will permit a perfect 

 correlation of that part of the Beekmantown formation with 

 the highly subdivided Lower Siluric of northern Europe. Fur- 

 thermore, as the graptolites changed so rapidly, and pelagic 

 forms are not subject to the slow^ migrations of the littoral 

 forms, but spread rapidly over wide territories, it is proper to 

 conclude that this Tetragraptus fauna, like the succeeding 

 faunas, conquered its territory in a very short time, and that 

 we have here, hence, not only homotaxial, but actually syn- 

 chronous beds of both hemispheres before us. 



The fact mentioned above, that the English and Swedish 

 faunas of this horizon have a greater number of species in 

 common than they have with the Levis fauna, is, in this connec- 

 tion, worthy of special notice, as it proves that a world-wide 

 and absolute identity of the pelagic graptolite faunas does not 

 exist. This may indicate that there also existed geographic 

 or regional differences, which, however, did not coincide with the 

 differences in the distribution of the other fossil organisms, as 

 has been suggested by Freeh [loc. cit. p. 116) in view of the 

 discrepancies observable in the succession of the two detailed 

 series of upper Siluric graptolite zones, made out by Tullberg 

 in Sweden and by Barrande in Bohemia. 



Zone with Didymograptus bifidus and Phyllograptus anna 



Graptolite hed 3 



This bed has a thickness of 2 feet, and is separated by 14 feet 

 of mostly barren limestone beds (bed h) from graptolite bed 2. 

 It has furnished, partly in an excellent state of preservation, the 

 following forms: 



1 Dendrograptus cf. divergens Hall r 



2 Dietyonema cf. delicatulum Daivson r 



3 Callograptus salteri Hall r 



4 Dichograptus octobrachiatus Hall r 



5 Goniograptus thureaui McCoy, var. c 



