To locate this EarthCache, you need to be down under the bridge, though there is no need to abseil down. The cache can only be done by accessing it from below. This bridge once crossed the Blackburn to Chorley line, which was last used in 1966. There may be some cachers who remember travelling on the line, if so, it would be great to hear your expreriences in your log.
Though we have not come here to discuss trains, that is another hobby, which may or may not interest you. I want you to look at the walls of the bridge. Now the bridge is made out of sandstone blocks, with mortar inbetween. It is the mortar that we are interested in, or rather what has occured as a result of it.
Mortar is traditionally a mix of lime and sand. Lime consists of calcium oxide, gained from heating limestone. At first there would have been neat lines of mortar between the sandstone blocks, but has time has gone on, and the structure has been exposed to water, the calcium oxide reacts with water to form calcium hydroxide. Over time, rainwater carries calcium hydroxide in a solution, which when it comes into contact with air, it reacts with carbon dioxide and calcium carbonate is preciptated. What you can see on the walls of the bridge is calcium carbonate.
In a cave the precipitation of calcium carbonate forms both staligtites and staligmites. Though in a location outwith of a cave, these deposits are known as calthemites. A calthemite is a deposit derived from concrete, lime or mortar, and they grow under ma made structures, and look like cave structures.
Calthemites can appear in many forms, which are :
Flowstones, which looks like a flowing river off calcium carbonate, this tends to be rippled.
Straw Staligtites, which are long thin straw like structures.
Calthemite staligmites, which are a build up of calcium carbonate on the floor, which gradually gain height.
Calthemite rimstones, these form on the floor as a gradually sloping structure.
When a staligtite and staligmite join, it is known as a column.
This being an earthcache, in order to log it, I ask that you answer some questions. Please send them to me, and do not include them in your log. You can send them to me by using the message facility or email, both of which can be found by looking at my profile.
1. Please look at the southern wall. What colour is the calthemite deposit? What does it feel like to the touch? How is it different from the sandstone block?
2. Please tell me which calthemite forms you can see?
3. If you can see a staligtite, please tell how long is the longest one that you can see?
4. Can you see any evidence of calthemite columns being formed, if so, how long are the columns?
5. What do you think will eventually cover the wall?