This earthcache will help you learn about limestone and fossils that can be seen in it.
You should be standing at the corner of St Vincent Street and West Nile Street, and looking at the panels on the wall in front of you.
Sedimentary rocks form as the result of sediment deposition (e.g. sand, mud, pebbles) by the action of wind or water, and as such are composed of layers (beds) of sediment. Some beds are laid down with the succeeding bed coming in at a slightly different angle; this is called cross-bedding. Geologists use this to tell if the rocks have been inverted or are still in their original setting. Sedimentary rocks can also form as the result of chemical or biological processes, which can produce rocks rich in calcium, such as limestone. Due to its calcite-rich nature, limestone is liable to weathering and as such does not make a long lasting building stone.
The shop is clad in pink limestone which is full of fossils, such as corals (but these are hard to spot) and the shelly fragments of bivalves and gastropods. There are irregular zig-zag boundaries which cut across the fossils: these are called stylolites and they formed fairly late in the history of the rock when mineral material was dissolved out by pressure.
Coral fossils
Corals comprise a soft-bodied animal called a polyp that lives in a calcareous skeleton or corallum. When the polyp dies, its soft tissues decay but the hard skeleton is left behind. This is what is preserved as a fossil.
Bivalve fossils
A bivalve fossil belongs to the phylum Mollusca and the class Bivalvia which have two hard, usually bowl-shaped shells enclosing the soft body. The tissue that joined the halves together decays over time, so rarely are the two halves found together.
Gastropod fossil
Gastropods are snail-like and slug-like invertebrates (lacking a backbone), and are types of molluscs. Since snails have hard mineral shells, they are the most common type of gastropod fossil.
Q1. Find an example of a bivalve fragment in the stone. Describe what you see in terms of colour, size and any distinguishing features.
Q2. Find an example of a gastropod fragment in the stone. Describe what you see in terms of colour, size and any distinguishing features.
Q3. From the information above, where do you think this limestone was formed? It may help if you consider where corals, bivalves and gastropods might all be found living together.
Q4. Please provide a photo of yourself or a personal item near GZ (without giving away the answers).
Answers to questions 1-3 should be sent by the message centre or email. Please DO NOT include the answers in your log.
Please send your answers BEFORE logging the cache. You do not need to wait for a reply, but if there is a problem, we will let you know.
ANY LOGS ENTERED WITHOUT ANSWERS BEING SENT WITHIN TWO WEEKS WILL BE DELETED.
