METHODS Piles of the
varicolored beds of the
lower Vernon Formation
are examined. From
beneath the piles, blocks of
gray to black shale and
mudstone are removed and
split as much as possible to
reveal fossil content. Note
the pit, dug by hand, from
which chunks, slabs and
blocks of rock were re-
Samuel J. Ciurca, Jr.
Rochester, New York
LEFT: One of the large blocks
of Pittsford Member extricated
from beneath the piles of lower
Vernon Formation debris. The
pile of small slabs can be
seen to the left. These rocks
yielded several fossils that are
important to an understanding
of the fauna and preservation
of features that indicate a little
about the paleoenvironment of
the region as it existed over
400 million years ago.
Except for the dolomitic units,
the shale and mudstone are
readily decomposed by rain
and exposure to the elements.
Intercalated dolomitic seams
help to keep some of the shale
layers (with fossils) intact.
Thousands of chunks of the
chunky shale and mudstone
were split to find specimens of
the Pittsford fauna.
RIGHT: A very large block
of the Pittsford Member
that was lifted out of one
of the rock piles. It was
quite difficult to break this
block along bedding
planes, but the rock was
full of eurypterid pieces
(tergites and other parts).
Note the gravelly nature
of most of the piles - this
is due to rapid decompo-
sition of the shale during
rainy periods producing
massive crumbling of the
The Vernon Formation In central New York, the Vernon Formation consists of over 500 feet of redbeds incorporating several thin units of dark shale,
mudstone and waterlime. The sequence not only bears several thin eurypterid horizons, but also an important Silurian fossil fish horizon. This formation is the
northern extension of an enormous deltaic deposit known as the Bloomsburg Formation in Pennsylvania. In New York, the redbed sequence is underlain by
150 - 200 feet of mostly crystalline dolostone, the Lockport Formation, with poorly preserved corals and stromatoporoids and a typical marine fauna indicating
widespread biostromal development preceding the incursion of very shallow waters at the margins of an advancing delta. Concomitantly, hypersaline waters
entrenched themselves within a sequence that resulted in cyclical salt beds being deposited. Most of the eurypterid horizons known within the state of New
York occur in units known to have had hypersaline conditions at least part of the time during their deposition. The Salina Group and overlying Bertie Group
are most notable.
LEFT: Posterior portion of a phyllocarid that I
retrieved on November 23, 2006. The first
frost froze the area for the first time, but the
warm weather of this November quickly
thawed out material so we could collect
additional material from the buried blocks of
the Pittsford Member. This specimen may
pertain to a Ceratiocaris, a common type of
phyllocarid known from Silurian rock.
LEFT: A bulldozer removes the
upper layers of rock that have
crumbled to small pieces and
exposes blocks and chunks of
the Pittsford Member that have
been 'protected' by overlying
debris. The dolomitic beds in
the original sequence are
more resistant to weathering
and degrade slowly - some
also protecting the fragile
black shale (and fossils) from
Without this bulldozing of the
overlying weathered material,
many fossil specimens would
have gone undiscovered. Many
specimens collected had to be
'stabilized' to prevent further
deteriorization by gluing some
specimens to cardboard or to
pieces of wood to prevent the
direct handling of material. Any
cracks that developed had to
be reinforced with glue.
BELOW LEFT: Large block of Chunky Bed being split. Note rind along edge with yellowish coloration - weathered zone. Many specimens
were collected from this type of lithology - a calcareous or dolomitic mudstone. Eurypterid remains are often preserved at all kinds of
attitudes to bedding planes - high energy or storm events seem most likely the cause for the distribution of eurypterid remains within this
type of deposit.
BELOW RIGHT: The Slate Bed - splits easily along bedding planes revealing mostly clean sheets of dark shale which, occasionally, bear
well-preserved eurypterids and other fossils. SALT HOPPERS occur commonly within this unit.
LEFT: A wonderful specimen of Hughmilleria
socialis preserving the ventral aspect and colored
yellowish by oxidation of iron compounds from
groundwaters percolating through the bedrock.
Note the smaller individual to the left with its
telson partly superimposed on the larger speci-
men. Somehow, the carbonized remains appear
to be more selectively replaced by the minerals.
The larger specimen is about 14 cm in length.
Note the large metastoma and the swimming leg
on the left. All specimens are believed to be molts
that were dumped into the Silurian muds during
storm intervals. Often, the eurypterid remains are
collected into windrows with exoskeleton parts
aligned parallel to the ancient shoreline - see
other photos on this site.
In recent years, the Pittsford Member of the
Vernon Formation has been exposed by several
construction projects, the Tastings Site being the
most recent. Only through such projects are we
able to get another glimpse of the wonderful
eurypterid fauna of the 'Pittsford Shale.'
Because of the peculiar occurrence of the fauna
within a sequence of rapidly changing lithologies,
it is quite likely that preservation occurs within a
mixed zone - i.e. where continental deposits
merge with the marine realm. It is conjectured
that Hughmilleria may have inhabited rivers and
that Eurypterus was more likely near-shore
marine and that both faunas were mixed in an
area of widespread mudflats along a Silurian
shoreline with nearby 'alglagoons' - shallow
bodies of water with cyanobacteria and subject to
Many thin lenticular dolostones intercalate with
beds of dark shale and mudstone - characteristic
features of the Pittsford Member. Eurypterid re-
mains appear in essentially all of the thin units
that comprise this member and are not restricted
simply to the "black shale."
Stratigraphic Chart - During the past several
years, more detailed knowledge of the indi-
vidual beds that constitute the lower units of
the Vernon Formation has been obtained.
One interpretation is provided by information
obtained directly from measurements made
at the Spring House Commons Site.
Prehistoric Pittsford - Several years ago, I
started my first website dealing with the great
eurypterids of the Silurian Period. While
some of it is outdated, now, you may still find
some items of interest: Prehistoric Pittsford.