On December 27, 2006, while driving on a holiday trip, I stopped at one
of my favorite fossil collecting spots near the interstate in Clearfield, Pennsylvania,
within a major bituminous coal mining region in the western part of the state.
This is an area of ridges and valleys, and the Pennsylvanian Period coal is in
layers on the ridges quite high above the valleys. Below is a view of the area
I visited. Much of the area is reclaimed land from the surface mines.

Click on pictures to Magnify

While looking around, I found a large boulder long-since exposed from the
coal mining activity, composed of a blue-grey massive [blocky] hard shale,
apparently formed from a clay layer that was below the coal [this has been
called the "fire clay beds", and it is located at the base of the Lower Productive
Coal Series] and this boulder had only underground plant parts in it. Two of
these stood out - a large vertical Stigmaria ficoides (Sternberg) Brongniart root
in natural growth position with rootlets spreading out at nearly 90 degree angles
from it, and next to it, the underground stem [rhizome] of a Calamites [giant
horsetail] plant. The matrix was very brittle and had been eroding awhile.

Calamites Calamites
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Above you can see the prominent underground stem, or rhizome, of the
that had grown into the mud next to a scale tree root [Stigmaria].
The Stigmaria root is not easily distinguished in the images above but it lies
just above the middle of the hammer and continues above and outside of the
image to the right. The Calamites rhizome was in the mud right next to it and
it narrowed a bit to the lower left - the aerial stem would have continued to the
right and above this rhizome reaching into the open air above the mud of the
swamp next to the scale tree trunk. This giant horsetail rhizome reminded me
a lot of the similar underground stems of the modern, but unrelated, bamboo
and some other large grasses. It seemed to me that while both plants are very
different and lived hundreds of millions of years apart in time, they seemed to look
and grow much like each other because they were living in a very similar environment.

Stigmaria ficoides Stigmaria ficoides
Stigmaria ficoides
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Above are two images of the Stigmaria root in its original position in the "mud"
with the Calamites rhizome next to it on the upper left. The second image has
been marked to show the general orientation of the rootlets that radiated from
the larger axis, and the scars on the main axis where many more rootlets were
once attached can also be seen. Stigmaria ficoides is a "form name" used for
the roots of several different genera and species of scale trees [including
and Sigillaria]. Unless the identifiable stems are found
attached to these roots, there is little way to know to which kind of scale tree
these roots belonged.

I was interested in adding this rather nicely preserved Calamites fossil to
my collection, but getting it home presented some difficulties. The boulder
weighed about the same as a small car, so moving it was out of the question!
The matrix was far too brittle to cut the fossil out with a rock saw [and I do
not have one anyway!]. So, I decided to extract the Calamites rhizome with
what I had, my chisels and hammers.

Click Here to Magnify

Above is the final result of this attempt to extract the fossil from the large
brittle boulder. I chipped the fossil from the boulder as carefully as I could,
and it came out in several pieces. I saved all of the pieces, and when I got
home I unwrapped them and had a pleasant afternoon gluing my puzzle back
together. While not easily seen in the image, some areas retained a carbon
"skin" which represented the original plant material, while the overall fossil
represents a cast of the internal pith of the rhizome. This fossil is shown
reversed from its original position in the boulder - this much better, more
detailed side was facing inward, and by extracting it I could now see the
better preserved, non-eroded face (the side not visible in the other images
shown above). This nicely preserved side of the rhizome could not be seen
if the block had been cut out of the boulder with a rock saw.

I do not know what species of Calamites this is - The lower stem pieces
and rhizomes are often called Calamites suckowii Brongniart, but the nodes
in my fossil seem too long for this. Calamites undulatus Sternberg, a wide
ranging species in the Appalachian area, is more likely. I welcome any
other opinions!

This was a pleasant exercise - certainly this is not the most amazing fossil,
but it was interesting to me because it was found in place in a "paleosol" or
ancient soil next to a tree lycopod root, and it shows that these two plants
certainly grew next to each other in the swamp - with even their roots and stems
intertwined. It helps one to picture this coal swamp forest when it was "alive".
It also was one of the first times I had the good sense to photograph the fossils
in place first so that the context and original positioning could be seen later.
This has made the fossil somewhat more understandable and living to me and,
perhaps, to you the reader.

Steven R. Hill

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