When in the area, there’s a number of local caches that are worthy of investigation, if you have the time, including Earthcaches by Mumbo Jumbo and Heidi Seekers.
On the second arch (north-east side of tunnel), look up, you will see a pretty good example of a stalactite, a formation more usually found hanging from the ceiling of caves and mines.
Limestone stalactites
Any material which can be dissolved or melted, can be deposited in the form of a stalactite; they may be composed of, among other materials, lava, minerals, mud, peat, or sand.
Usually stalactites are found in limestone caves. Simplistically, they form through deposition of minerals (usually calcium carbonate) which is dissolved in water running through the rocks then precipitated from the resultant solution. This solution travels through the rock until it reaches an edge and if this is on the roof of a cave it will drip down. When the solution comes into contact with air the chemical reaction that created it is reversed and particles of calcite (calcium carbonate) are deposited. An average growth rate is 0.13 mm (0.0051 inches) a year. The quickest growing stalactites are those formed by fast-flowing water rich in calcium carbonate and carbon dioxide, these can grow at 3 mm (0.12 inches) per year. All limestone stalactites begin with a mineral-laden drop of water. When the drop falls, it deposits tiny amount of calcite. Each subsequent drop that forms and falls deposits more calcite. Eventually, as more calcite is deposited, the familiar cone-shaped stalactite develops. The same water drops that fall from the tip of a stalactite deposit more calcite on the floor below, eventually resulting in a rounded or cone-shaped stalagmite.
Concrete stalactites
Stalactites can also form on concrete, or even plumbing where there is a slow leak or permeation of water, and there is limestone (or other minerals) in the water. The chemistry of how stalactites form on concrete is slightly different to those formed in limestone caves but the general principle involves dissolution and re-deposition of minerals (invariably Calcium Carbonate).
Flowstone
Further along this tunnel, there are also embryonic examples of flowstone; these are composed of sheet-like deposits of calcium carbonate. This is formed where water flows down the walls rather than drips from the ceiling. Again, they are much more common in limestone caves. The deposits may form thin sheets called "curtains"; some have brown and beige layers that look much like bacon (often termed "cave bacon").
To log this cache; please provide answers to the following questions via my link, above:
1) Estimate the ‘height’ of the longest part of the stalactite
2) If the growth rate for these objects is in the region of 0.1 to 0.2 millimetres per year when they are underground, how old would that make the stalactite here?
3) Does this age fit with the location? Or does this suggest these objects are growing at a faster or slower rate?
