338 The American Geologist. December, 1908. 
Hamilton faunas would be a problem too large and too wide- 
reacbing for introduction bere. But most probably botb came 
from tbe east and both had most likely been in existence on 
the eastern shore of the Appalachian gulf during no small part 
of the previous period. The almost complete destruction of the 
shore-line that has since taken place renders it impossible at 
present to detect and to prove this contemporaneity, but there 
can scarcely be a doubt that the Marcellus fauna overlapped 
downward in the east, in some places where favorable con- 
ditions prevailed, even during the Corniferous period, since it 
must have had both time and place for development before it 
emerged ; and we shall later see that it continued upward long 
after the Alarcellus period had closed. 
As a further illustration of the same principle of the per- 
sistence of tbe faunas in the Devonian era, we quote professor 
Hall, who writes : * 
"At Ithaca, where we an: far above the Tully limestone, and where 
the rocks are well marked by an abundance of fossils peculiar to them- 
selves, we still find Mtcrodon bellistriatus, Moaiola concentricus and 
some others, and I have even detected Calymene bufo and Dipleura 
dekayi in the same association." 
These are all Hamiltonian species in New York, and yet 
they occur far above their normal limits and indicate a sim- 
ilar persistence of some members of that fauna to much later 
times. Reverting to the Marcellus, professor Hall remarks of 
the fossils of the Genessee shale :f 
"The three species here figured Avicula (Luiiulicardiitm) fragile, 
Strophomena (Chonctcs) setigerus, Tentacitlitcs (Styliola) UssurcV.a 
are common to this rock and the Marcellus shale, the lithological char- 
acter of the two being precisely similar. Neither of them has been 
noticed in the intervening rocks of the Hamilton group, though the 
Avicula passes upwards into the Cashaqua Shale cf the Portage group. 
This is an interesting example of the recurrence of the same species of 
fossils in rocks widely separateu from each other." 
This observation of professor Hall carries three of the 
Marcellus species up through the Hamilton (though not yet 
found), through the Tully and into the overlying Genesee. 
Professor H. S. Williams in a paper read before tbe Ameri • 
can Association for the Advancement of Science, at Cincinnati, 
* Geology of the Fourth District of New York. p. 21' 
t Op. cit.. p. 222. 
