RAYMOND: CORRELATION OF THE ORDOVICIAN STRATA. 23] 
is, however, not yet fully settled, though evidence accumulated by 
Dr. Ulrich (119) shows that the Lévis 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, Phyllograptus ‘licifolius, 
P. angustifolius, Didymograptus bifidus, and D. amplus have been found 
with brachiopods and fragments of trilobites. Ina bed just above the 
one containing graptolites, Plethospira cassina, Subulites obesus, and 
Eurystomites kellogt 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 Lévis 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 Lévis, but 
Didymograptus bifidus is found in shale in the middle of the section. 
The fossils in Arkansas thus suggest that the middle of the Lévis 
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) (A:-B,,,) of Russia 
are equivalent to the strata from the Dictyonema zone to the Gigas 
limestone of Scandinavia and to the Canadian (Beekmantown) of 
America. 
