12 
laurentina has not been seen, but A. marginalis has been col- 
lected above the coral and Beatricia zones. Parastrophia 
reversa is present in tens of thousands of individuals in the ex- 
posures of the south shore, existing in the rocks in about the 
position in which they lived upon the bottom. About a half 
dozen worn and washed specimens have been found on the north 
side. A species associated on the south side with P. reversa is 
Hebertella maria. The writer does not recall having seen it on 
the north side. The coral zone on the south side contains 
Halysites catenularia in abundance. It hardly makes its presence 
felt on the north. A Syringopora occurs associated with the 
corals in the Vaurial section and the section of the north shore. 
The writer has not seen it on the south. At cape James Liospira 
Helena occurs in the zone filling a channel in abundance. It 
has not been seen on the south. On the north shore is a bed 
near the top of the formation filled with what appear to be 
calcareous algae. Nothing similar was seen on the south side. 
On the south shore the initial formation of the Silurian, the 
Becsie River, is characterized by an abundance of Pheenopora ex- 
pansa and Virgiana barrandei . The former is equally abundant 
in the exposures of the north side and Vaurial river, but of the 
latter not more than three worn specimens have been collected, 
and two of these are doubtful. On both shores the basal portions 
of the formation consist of limestone in which are many zones of 
limestone conglomerate. On the south shore the character of 
the deposit continues unchanged to the top of the formation, 
but on the north shore the upper portion of the formation con- 
tains a thick zone of dark shales in which there is an abundance 
of Camarotcechia glacialis and C. fringilla. Small specimens of 
these shells have also been found in the southern exposures, but 
they are not common. Both species were evidently inhabitants 
of muddy bottoms. 
The Gun River formation consists largely of limestone which 
on both shores contains an abundance of pebbles and boulders 
of limestone. The faunas of both shores are also similar. 
The Jupiter River formation makes its appearance on the 
north shore just around the east end of the island and thence 
