This Earthcache focuses on the features & origins of Fossil Wood
Published to mark Earthcache Day on 8th Oct 2023
Kinneil House is a Category A listed historic house to the west of Bo'Ness, in what was the original settlement of Bo'ness area - Kinneil Village. It was once the principal seat of the powerful Hamilton family in the east of Scotland and is linked to several major events in Scottish history, politics, culture and particularly industrial development (the workshop of the inventor James Watt is next to the published coordinates). The last permanent resident of Kinneil house was Professor Dugald Stewart, an 18th Century polymath and major figure in the Scottish Enlightenment. The house however, is said to be haunted by The White Lady - the ghost of Lady Alice Lilbourne, who in the 17th Century fell to her death from one of the building’s top-floor windows.
Lady Lilbourne was the wife of a Cromwellian General who was stationed at Kinneil House. The story goes that the marriage was not a happy one, and Lady Alice was locked into an attic room overlooking the rocky ravine and burn below. Apparently, she managed to escape in a white nightgown, but was quickly recaptured. In desperation she flung herself out of the window to her death into the deep rivine next to the house. almost 200 feet down. The writer Maria Edgeworth visited Professor Stewart and his wife in 1823 and gives this account of her visit:
“Mrs. Stewart told us this morning that there were plenty of ghosts at our service belonging to Kinneil House. One in particular, Lady Lilburn (sic), who is often seen all in white, as a ghost should be, and with white wings, fluttering on the top of the castle, from whence she leaps into the sea – a prodigious leap of three or four hundred yards, nothing for a well-bred ghost.”
Local folklore has it that when Lady Lilbourne fell to her death, into the tree-lined rivine below, a drop of her blood fell on a tree-stump and turned it to stone.....
At the published coordinates near Kinneil House, you will see a collection of large stones that seem to have been placed for ornamental purposes. They are sitting opposite the shell of a small building where the famous inventor James Watt conducted his experiments.
Look closely and you will see that one of the stones sitting apart from the main cluster of stones, looks a lot like part of a tree trunk - it's the one furthest north marked with an 'X' in the picture below, and sits closest to Kinneil House. There's a 30-year old hard copy photo of this stone tree trunk in Falkirk Museum Archive, and it records it as a posssible example of a Petrified Tree.
The Kinneil Stones
Unlike other plant fossils, which are typically impressions or compressions, petrified wood is a three-dimensional representation of the original organic material. Sometimes there are traces of the original organic material still present. Petrified wood is most commonly associated with trees that were buried in fine grained sediments of deltas and floodplains, or volcanic ash beds.
Typical Petrified Tree Trunk
It's difficult to say how this stone tree trunk got here, it may have been a curio brought to Kinneil, or maybe found in the wider area. However the area is known for occasionally producing fossil tree evidence, and local collectors have unearthed several examples of Stigmaria (the fossilised roots of trees) at the original mouth of the River Carron a few miles away. So the local conditions were once suitable for creating fossil trees.
This fossil may look like the trunk of a tree but it's actually from an ancient form of giant fern. It dates from the Carboniferous Period, some 320 million years ago when this area was near the equator and would have looked more like a jungle. Kinneil then would have been a tropical rainforest populated by large lizard creatures, massive centipedes and huge dragonflies. Carboniferous forests contained some of the earliest plants, including giant ferns and huge trees far distant from what we have now. Modern trees, which are essentially flowering plants, evolved much later, in the Cretaceous Period, that began 145 million years ago.
Carboniferous Period - Giant Fern
Petrified trees are in fact created by a complicated process where the conditions have to be just right. The usual steps involved are that firstly, a deceased tree (or giant fern) needs to be covered in mud, sand, or even volcanic ash shortly after falling to the ground. Ash would typically colour the fossil differing shades of grey, sand would colour it mid/light brown. This covering substance protected the dead giant fern from oxygen, which is one of the main causes of the decaying process. As a result it decomposed far slower than normal.
The next step in making a petrified tree is a process known as Permineralization, which occurs while a tree lies coated and preserved in sand or ash. This process involves deposits of minerals into the cells of the tree. Water from the ground, lakes, or oceans seeps into the pores of organic tissue and forms a crystal cast with deposited minerals. Crystals begin to form in the porous cell walls. This process continues on the inner surface of the walls until the central cavity of the cell, is completely filled. The cell walls themselves remain intact surrounding the crystals. Over a period of a few million years, those minerals will totally crystalize.
The end result of permineralization is a rock that appropriates the shape and structure of the original tree. Fossil woods created through permineralisation are very close replicas of the original tree, almost to a cellular level. So if you do a cross-section of the fossil it will look similar to the cross section of a real tree. However, a petrified tree trunk is easily differentiated from real parts of trees, because petrified wood is very hard, but brittle. It can shatter like glass, but as a whole, it is as strong as steel. Petrified wood rates 7.8 on Mohs Hardness Scale, and is also very heavy, typically weighing between 160-200 pounds per cubic foot.
Maybe. There are other ways a tree trunk can become a fossil.
Some natural events like severe storms and floods can move the trunk of a tree (or a giant fern...) considerable distances. If that trunk ultimately gets located in a silty or sandy environment, the tiny elements of sediment can surround the trunk, burying and preserving it, much like when petrification happens. When the sediment hardens over millenia into rock, it will form a three-dimensional negative or mold, of the tree trunk.
In this Cast and Mold method of fossil creation, the trunk decomposes as the surrounding sediment hardens, then water filters through the sediment, leaching out the organic remains and leaving a void containing a detailed structure of the organism called a negative or external imprint. That imprint acts like a mold when silt or sand begins to fill the void left, and that silt/sand can then solidify into rock over millenia. The surface of the cast and the mold fossil can be a good copy of the original tree, but no actual tree material remains. This differentiates it from petrified wood, where the fossil can be a copy of the original tree material, right down to the cellular/microscopic level. So a Cast and Mold fossil is probably the mode of preservation that gives the least detail of the wood. It wouldn't look like a tree cross section if you were to cut it in half and examined the interior.
To claim this Earthcache as found, send me your answers to the following 3 questions, via the Geocaching app or the website. This must be done before logging the cache. I will reply to all your answers.
1) Describe the fossil wood here in terms of it's it's colours, textures (hard/soft, smooth/contoured), and shape. Look closely, is there any evidence that the fossil is brittle?
2) Based on the colour, do you think it was ash or sand that covered up this tree trunk and helped cause its fossilisation?
3) Look at the ends of the tree trunk, do you think this is Petrified Tree trunk or a Cast and Mold fossil? Why do you think that?
As an optional task please post a picture of yourself, or some identifying item, with Kinneil House or Watt's Cottage in the background. Please don't include the fossil in the picture. This task is not necessary to claim the cache as found.
As additional homework you may want to take a look at the stone lying on the ground in the foreground of the picture as well, it also has an interesting appearance.
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Thanks go to Mark Wilkinson, President of The Edinburgh Geological Society, for his invaluable assistance in creating this Earthcache and identifying the Fossil.