RAYMOND: CORREL.\TIOX OF THE ORDOVICIAN STR.\TA. 231 



is, however, not yet fully settled, though evidence accumulated by 

 Dr. Ulrich (119) shows that the Levis and Beekmantown are probably 

 of the same age. This evidence is based largely on the occurrence of 

 graptolites in dolomite with a Beekmantown fauna near Smithville, 

 Lawrence Co., Arkansas. At this locality, PhyUograptu^ ilicifolius, 

 P.angustifolius, Didymograptiis bifida^, and D. amplus have been found 

 with brachiopods and fragments of trilobites. In a bed just above the 

 one containing graptolites, Plethospira ca^sina, Subulites obesus, and 

 Eurystomiics kellogi were found. These latter fossils are characteristic 

 of the Cassin limestone and occur about midway in the section of the 

 Beekmantown on the eastern side of Lake Champlain. In Vermont 

 the strata of the Beekmantown are principally limestone and dolomite, 

 the total thickness being about 1200 feet, the top being unknown, as 

 the upper beds were eroded before the deposition of the Chazy. The 

 top of the Cassin limestone is 470 feet below the top of the Beekman- 

 town and the formation is 100 feet thick. No graptolites have been 

 found in the Beekmantown in Vermont. There seems no doubt 

 however, that the mollusks cited above are characteristic of the Cassin 

 and, therefore, the graptolites found in Arkansas belong in the Cassin 

 or in an older formation, and are surely Beekmantown in age. 



In England all the species of Phyllograptus and Tetragraptus are 

 in the Arenig, and in America the various zones of the Levis contain 

 species of these genera, and all the zones are so knit together by com- 

 mon species that it seems quite evident that all belong to a continuous 

 series. Phyllograptus ilicifolius is a long ranging species at Le^'is, but 

 Didymograptus bifidus is found in shale in the middle of the section. 

 The fossils in Arkansas thus suggest that the middle of the Levis 

 corresponds to the middle of the Beekmantown, and that the two are 

 approximately equivalent. 



From these considerations one feels justified in concluding that all 

 the strata characterized by Phyllograptus, Didymograptus bifidus, 

 and Tetragraptus, both in Europe and America, are equivalent, and 

 represent the deposits of Beekmantown (Arenig) time. It has been 

 pointed out in the previous detailed discussions that the Dictyonema 

 and Ceratopyge zones of Scandinavia are related to the strata over- 

 lying them, so that the final correlation would be that the formations 

 from the Packerort to Kunda (inclusive of both) (A2-B111) of Russia 

 are eciuivalent to the strata from the Dictyonema zone to the Gigas 

 limestone of Scandinavia and to the Canadian (Beekmantown) of 

 America. 



