Petrified Wood

closeup of petrified wood

The petrified, or fossilized trees of Prince William Forest Park are believed to be that of Taxodium distichum, or what we know as the Bald Cypress. Part of this opinion is founded in the fact that the fossil trees were found in the only area within the park where Cretaceous period sediments are found, that being the northeastern corner of the park. Taxodium were proliferate during the region during that the Cretaceous period, and a side-by-side comparison of the fossils against their present-day counterparts makes the distinction rather easy. Read our full report, A Petrified Prospectus, created by Geoscientist-in-Park Volunteer, Eric Junger.


When was the Petrified Tree Alive?

Scientific data suggests that the earth is 4.6 billion years old; to put that into perspective, if that entire timeframe were to be compressed into a 24-hour period than humans as a species have only existed for approximately 10 seconds. This immense timeframe has been divided into various eons, periods and epochs as a way of understanding the variations of life and climate that existed in this changing world.

The Cretaceous Period ended approximately 65 million years ago and spanned a period of 79 million years. The Cretaceous Period was considered by many to be the height of the gigantic animal evolution, which would suddenly end in catastrophe and near desolation of 85% of all life on the planet. At the end of the Cretaceous period virtually all dinosaurs were wiped out, and debate still rages today as to how this happened. This time period is when the petrified wood at Prince William Forest Park was alive and growing as a tree.


The Cretaceous Climate

During the portion of the Cretaceous period when our fossil trees were growing, Virginia was largely swamps with tremendously high humidity and daily temperatures over 100° daily. The swamp-like environment, coupled with the touching landmasses, allowed for a broad distribution of animals and explains why the same sorts of fossils found along the coast of Africa.


How Did the Wood Turn to 'Stone'?

In order for a plant to be fossilized, oxygen must be removed from the plants environment. Though this can happen in many ways (such as fire or volcanic explosions), in the case of our petrified wood, this occurred when the ancestral bald cypress trees fell over into the dense mud of their tropical environment. The lack of oxygen in this environment is called anaerobic. It is necessary to fossilize the wood because most bacteria, insects and other decomposers require oxygen to decompose the organic material of the tree.

Finally, through pressure and time, other minerals such as silica replace the cell material in the tree and are hardened into the petrified trees we see today.

the fossilized tap root of petrified wood tree

About Our Petrified Tree

Bald cypress is a large, slow-growing but long-lived, deciduous conifer, which frequently reaches 100 to 120 feet in height and 3 to 6 feet in diameter. Its trunk is massive, tapered and buttressed. The leaves are alternate, linear and flat with blades generally spreading around the twig. The bark is thin and fibrous with an interwoven pattern of narrow flat ridges and narrow furrows. Its male and female flowers form slender tassle-like structures near the edge of the branchlets. Bald cypress trees produce cone fruit, and there are approximately 5,200 seeds per pound. It develops a taproot as well as horizontal roots that lie just below the surface and extend 20 to 50 feet before bending down. It develops knees that grow above water providing additional support.

An examination of the base of the large trunk section of the fossil tree easily demonstrates the taproot of the tree, and in the picture to the left a fine layer of quartz has developed within the inner wall of the taproot, which typically has a sort of void within its structure, allowing for the larger crystal formation over time during petrification.

rings on petrified wood tree

How Old was the Tree When it Fell?

The larger of the two specimens, which has the truck section intact and is located outside of the visitor center, measures an average of two feet in diameter at the distal (narrow) end and 3'4" to 4'6" in variation across the bottom of the trunk. The length of the large specimen is approximately 6' on the average. On the distal end is a section of rings that are clearly visible and cover approximately 5" of radius before the mineralization of the tree obliterates the ring structures. There is a distinct bark ring surrounding the large specimen which varies in thickness between 1-1/2" to 1-3/4" and almost 3" thick on the trunk end. Allowing for this thick bark at the distal end, there is then a total of 40 rings clearly seen in the five inches of radius that is visible. Assuming that the rate of growth of the tree was normal and regular, without droughts or other interferences, we can say that the ring density is approximately eight rings per inch, given 40 rings within 5 inches seen. With a radius of 12 inches, subtracting 1 inch for bark, that would give us 11" of tree left, placing the approximate age of the tree at around 88-90 years of age before falling.

There are no rings visible on the other fossil (located outside of the Turkey Run Education Center) due to the mineralization and likely fracture of the ends at time of collapse. Because these fractured ends will lead to a blurring of rings and heavier mineralization, a more accurate ring count can be made in both cases by making a cross-section of each of the specimens perpendicular to the long axis of the specimens. Calculating the circumference of the second specimen using geometric formulas it is determined that the fossil has a circumference of a minimum of 6'. The diameter is an estimate because there are deformities in the outer surface of the tree with unequal mineralization.

Last updated: October 5, 2017

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