ANTICOSTI ISLAND FAUNAS. 
11 
Silurian System , Anticosti Series. 
Becsie River Formation. The passage from the Ellis Bay 
to the Becsie River formation witnesses the extinction of about 
eighty per cent of the Ellis Bay fauna and the major portion 
of this extinction takes place in the upper three zones, which 
in their rapid lithic and faunal changes presage the initiation 
of a new geologic cycle; but beginning with the first zone of 
the Becsie River formation, stability of sedimentation and fauna 
is again instituted. Beyond the faunal evidence, there is 
none other, either structural or depositional, suggesting a stra- 
tigraphic break and the faunal change can not be taken to in- 
dicate any interruption of deposition, since it can as readily 
be explained by a change in ecology which may have been brought 
about by some physical event in a region comparatively distant, 
and until more is known of the factors that determine the char- 
acters of faunas, the causes of their local extinction and the re- 
placement of one by another, it appears to the writer to be idle 
to assume that faunal changes are indicative of breaks unless 
they are accompanied by other evidence. Since no strati- 
graphic break has been ascertained, the base of the BeCsie River 
formation and the Silurian has been somewhat arbitrarily 
placed where there is the most decided faunal and lithic change. 
In the earlier paper by Schuchert and Twenhofel, the 
writers were inclined to the opinion that the early Silurian 
beds of Anticosti could be embraced within the series term 
Niagaran. This view has now been abandoned, since it appears 
that it would give the term too great an extension beyond its 
original application. 
Savage has lately proposed the series term Alexandrian for 
certain early Silurian deposits of southwestern Illinois and 
eastern Missouri, the series to embrace all deposits between the 
Ordovician and the Clinton 1 . In 1857, Billings proposed to 
place all the Anticosti section above what is now defined as the 
Charleton formation in a new group which he proposed to call 
the Anticosti group, considering this portion of the Anticosti 
section as holding a position intermediate between the Ordo- 
1 Savage, Bull. Geol. Soc. Am., Vol, 24, 1913, p. 351, 
