Petrified wood caught our
attention this month due to an old “cedar” fence post that we have stored
here. Now, how many of you have an old
fence post that you have had stashed away for years? More on that later, but for now, what the
heck is petrified wood? The word comes
from the Greek language, where petro means stone or rock. In fact, variations of the word petro show up
in place names and even the names of people.
We know a person in San Marcos whose first name is Petra, of Dutch
origin.
So, petrified wood is
where the organic material is replaced with inorganic material over long
periods of time. The process is called
permineralization. This process occurs
when mineral laden water slowly replaces
organic material as it decays. It must
occur slowly because if the wood decomposes rapidly---let’s say to rot or to be
eaten by termites, there is no time for the slow process of permineralization
to replace the organic cell structure. This replacement process must therefore
occur underground where there is no oxygen to facilitate the rapid decay of
wood cells.
The “recipe” for
petrifaction then is (a) an environment with very little oxygen—probably not
zero oxygen, but close to it (b) mineral laden water, and (c) time, lots of
time.
The environment of very
little oxygen usually exists several feet underground. Wood occurring underground usually happens
due to sedimentation where soil is deposited on top of forests materials. For example, Exxon plastics plant contracted
with a gas well driller to place a well on company property at Mont Belvieu,
northeast of Houston years ago. The site
was about a mile away from Cedar Bayou.
I often would go to the drillers control room and chat about the process
of drilling and one day he said that he found something interesting. At about 40 feet down, soon after the start
of drilling, he came upon a cypress log or stump because his drill bit kept
bringing up bits of wood. Thousands of
years ago, this was probably a tree growing on the banks of Cedar Bayou, now a
mile way. So over many years, the bayou
changed course and lots of sediment overfilled the area. You can bet this wood was on its way to
becoming petrified wood. All that it lacked was time, lots of time.
The minerals in this
process of permineralization are mainly silicates and for the most part are not
colorful. But some petrified wood is
colorful and it is due to trace impurities in the mineral water—impurities,
mainly metals such as chromium, copper, zinc, manganese, etc. The petrification process provides
paleontologists with a lot of information because the process of petrifaction
reproduces the cell structure of organic materials in great detail. Thus when we see a petrified log, we can
tell what kind of tree existed in the area from just examining the cell
structure. From these studies, we know that palm trees grew in Texas thousands
of years ago and we know from the petrified dung of dinosaurs what they had for
lunch.
Petrified wood can be
found nearly everywhere in the world. In some localities it is so abundant and
undisturbed that governments have protected these artifacts by creating
preserves. One such preserve in the
United States is in Arizona, the Petrified Forest National Park. Here, whole logs in sizeable lengths can be
easily viewed on the surface. Here is one such example from the National
Forest:
Arizona petrified wood is
especially colorful and so it was a good move to create this National Park as
these specimens were rapidly disappearing due to their value in polishing the
surface to show the beauty of the stone and selling them as bookends, etc. A
search of the internet would suggest that a five pound chunk of this colorful
wood might cost up to a thousand dollars today.
Forty years ago, when we did most of our collecting, we bought really
colorful petrified wood for no more than a dollar per pound. Here is one piece still hanging around.
Petrified wood can be
found in nearly every part of Texas, some places easier than others. In some areas, it can be found on the surface,
but only in small pieces. In other areas,
such as in east Texas, it occurs in larger pieces, but usually one has to
either dig for it, or search along the sides of riverbanks, road cuts or any
excavations that reveal pieces of stone.
Here is a photo of a nice piece of palm wood that we found in the Lake
Livingston area of our state when the excavation for the reservoir was
underway.
Below is a photo of another
chunk, not very colorful, from the same area, and from an unknown wood. Both these chunks of wood each weigh about
five pounds.
Although petrified wood
can be found in nearly every part of Texas, it is more commonly found in a band
that courses through east Texas then
curves southward to the Rio Grande.
Pulling up the surface geology map we used in the geology discussion, it’s
where the rocks from the Cenozoic era are on the surface or near the surface. These are the rocks that are from 40 to 60
million years old.
The petrified wood zone of
most interest is the dark- brown band that courses from the Sabine to the Rio
Grande.[1]
If the Permian Highway Gas
Pipeline ever gets through this area, it will surely be interesting to see what
the trenching machine unearths as it progresses through the region to the east
of here. A nine foot deep trench should
provide some good prospecting.
Now back to the fencepost. As I was replacing fence posts in Medina
years ago, I noted that some that were being pulled out of the ground were
heavy for their size. I put one aside
and saved it. The posts were in the
ground for at least the last 80 years.
They were not rotting, nor termite chewed, just weathered. This one calculates to have a specific
gravity of about 1.14 which means the wood will not float in water. Why is this wood so heavy? Most likely, water
from the ground saturated with silica was pulled up by capillary action into the
post. The water evaporated and left the
silica in the pores of the wood. This
post must be a small fraction of the way to being a petrified log. But it would never make it for the million
year trip because just weathering would make it disappear long before petrifaction
could occur.
Interesting, nevertheless.
History
of the Area (continued)
In an earlier edition,
roads in the area were one of the subjects and now we have some more specific
information.
Roads in the time when
Hays County was first settled were trails more than they were roads as we now
might define a road. When the state
first became organized to the extent that it had a road department, the road
department issued standards for new roads.
One standard was that when the roadbed was cleared, the trees that were cleared
had to be cut so that the stumps that remained were not more than 6 inches
high.
Here is a copy of the map
(Map No. 16848 from Texas GLO) of our area.
The map is dated 1880, long before the advent of cars, so these roads
are trails for wagons, cattle herds, and horses.
If
you can expand the view, you will see that there are two roads that leave San
Marcos and travel west. One, the lower
one, is labeled Purgatory Road; the upper one is labeled Wimberley Road. These two roads are one as they leave San
Marcos, but split soon after leaving San Marcos. It appears that they may have parted where
the Fulton Ranch Road branches off from RR 12 today. The Road to Purgatory then continues on what
is now Hugo Road. So why did the early
settlers choose the Hugo Road track instead of the RR12 (of today) to get to
Purgatory Springs? For at least two
reasons: (1) trail blazers always
followed stream beds to have the best chance at water supplies for
themselves and their horses and (2)
following stream beds usually gives a path with a more or less constant
grade. If you drive to Purgatory Springs
area (the intersection of current Purgatory Road and RR 32) via Hugo Road,
there are fewer steep grades and reversals than if you drive to Purgatory via
today’s RR 12/RR 32.
We
are still looking for original source information on the origin of the name
Hugo. We do know that the original name
for the area was Purgatory Springs, then it became Hugo. Our focus at the moment is the USPS records
where we learned that the Purgatory Springs P.O. was in operation from June
1890 to August 1895 when it closed and all mail was directed to Fischer
Store. Only a year later, November 1896
the Hugo Post office was opened, probably in the same store where the Purgatory
Springs P.O. was a year earlier. What we
are trying to determine is what caused the renaming of the reopened post
office. One reason could be traced to
Postmaster General Order114 issued in 1849 that
. . . “from this date only short names or names of one word will be
accepted.” Many other additions such as “.
. . store, station, springs, etc. were considered objectionable”. Purgatory by
itself could have been objected to by the USPS and the community itself. Local oral history says that it was named Hugo
after a family ancestry of the 1300’s but we need to substantiate this if
possible. Incidentally, this newly opened post office only lasted 12
years. When it closed, all mail was
directed out of San Marcos.
Sightings
The
wild plum trees are blooming this week.
Here is ours; it is this tree’s first ever bloom being only 6 years old.
It was started from a plum that had fallen to the ground.
There are two other wild
plum trees blooming, one just to the west of the Upshaw property and another on
the Miller property. They are easy to spot because of the abundance of white
blooms when nothing else is showing.
R & D
Tusch
[1] Do
an internet search for rock hounding Texas San Jacinto River for petrified wood
and several videos will come up.
