At this location you will find a piece of petrified wood that was found in the Portland Quarry in Purbeck..
Petrified wood occurs when a tree (woody stem) is buried in wet sediments saturated with dissolved minerals for example by landslide or other occurrence. The lack of oxygen slows decay of the wood, allowing minerals to replace cell walls and to fill void spaces in the wood. Left undisturbed for thousands of years, the cells of the wood are slowly replaced by minerals carried in ground water. Groundwater rich in dissolved solids flows through the sediment, replacing the original plant material with silica, calcite, pyrite, or another inorganic material such as opal. This process of permineralization happens when all the the organic matter is completely replaced by minerals, it is turned to stone (petros), a process known as petrification. This means that often the grain of the tree can be found in the rock. Colour can indicate what trace elements or minerals are present within petrified wood. Some examples can include red, orange and yellow indicating iron oxide, pale purples and pinks could indicate manganese, and blue and green colors can suggest copper, chromium or cobalt.
The Purbeck trees seem to have been an early type of cypress or juniper type. These trees were apparently common in Jurassic times in what is now the UK area.
On the Jurassic Coast trees were dying out because of rising water levels, as the water evaporated in the heat, the minerals in it, included silica became concentrated. The remaining tree stumps absorbed the minerals which preserved them as fossils. At this location you will find the fossilised stump of a coniferous tree which would have been growing on Portland at a time (over 135 million years ago) when it was on the edge of a freshwater lagoon that stretched part-way across France. The continent was much further south than it is now, on a level with Cairo and it would have been much warmer, with tropical forests, the earth teeming with dragonflies and beetles we would recognise and dinosaurs we would not. As the freshwater evaporated, leaving salty water, the fallen tree absorbed silica, enabling it to be preserved, rather than rotting away.
If this small example of petrifies wood has peaked your interest, then you could plan a trip further South where you can find the remains of a fossil forest on the cliff edge to the SE of Lulworth Cove.
At this location there is a tree stump (from a Pine tree) from Portland that was placed in 2009. There is an information board near the sign that may prove helpful. It even made the local news.
Observe, the colour and texture of the rock - if you look closely you can see the impression of the grain of the tree:
a. Name at least 3 colours that you can find in the stone.
b. Which minerals do you think are most likely to be present in this stone. Explain your answer.
c. Describe how this petrified wood was most likely formed?
d. (Optional) – post a black and white picture of the you/or part of you at the location.
Once found, please log the cache and send you answers to the CO with your answers. If your answers are not correct the CO will reply.