Please look at the spolier images carefully before you start searching, the tube-worm effected rocks and rock coral are quite similar.
At the location given you will find yourself on a beach. At the bottom of the sand hills you will notice a small section of large pebbles that have been gathered here by the action of the high-tides. These pebbles ranging from the size of a house brick to much smaller are rolled up and down the beach by the action of the waves and so you will notice are round or ovoid in shape.
What I want you to do is search in these pebbles for rocks which have hundreds of little irregular holes in them, but are not the ones made by tube worms. The ones you need to find look like they are made up of lace made out of rock. What you have found is a piece of fossilised coral form an ancient sea.
I have attached a couple of images of the wrong type of rock, these are labeled tube worms, they have nice smooth holes that look like they have been drilled. Most of the tube worm effected rocks are grey at this location. Ignore these rocks and look for the lacy ones.
I have added a photo of the type of rock you are looking for, this is called rock coral. The ones you are looking for are a yellow rock at this location.
Corals are made up of small invertebrate animals, known as zooids, that look like tiny sea anemones. They feed on small food particles they find in the water around them.
Together, many zooids form colonies, many colonies form reefs. Coral reefs can be massive structures, stretching hundreds of miles. The Great Barrier Reef in northern Australia can be seen from space.
The oldest coral fossils are over 500 million years old. The earliest forms were different from those we see today and they died out 225 million years ago. Modern corals are still common in tropical oceans.
Corals are very important fossils. Many corals have a hard exoskeleton made of calcium carbonate. It is this exoskeleton that is usually fossilised. When the coral dies, the skeleton can be broken down to form limestone, an important building stone.
They type of corral you can fine here are called Halysites.
Halysites (meaning chain coral) is an extinct genus of tabulate coral. Tablulate coming from table, or flat in nature, they are almost always colonial, forming colonies of individual hexagonal cells known as corolites defined by a shell or skeleton of calcite, similar in appearance to a honeycomb, like bees make. Adjacent cells are joined by small pores. Colonies range from less than one cm long to meters in diameter, and they fed upon plankton.
The coral pieces you can find here today are part of much larger coral structures which died and were fossilised. You find them on this beach because they have been broken off by water action and rolled about on the beach exposing the fine structure of their skeletal remains.
These tabulate corals lived from Ordovician to Silurian (from 449.5 to 412.3 Mya). Fossils of Halysites species have been found in the sediments of Canada, United States, Poland and Australia.
Questions
- Please find a piece or several pieces of fossilised coral and describe what they look like, concentrate on the number of holes, their shape and the colour of the rock.
- Please explain why you think there are pieces of coral here and why they are smooth on the surface and not sharp and jagged as they would have been when they were alive.
- Please describe the state of the tide, the time you visited and how far the pebble shelf was from the water’s edge when you visited.
If you feel willing and able, please include a photo in your log of the fossils you found and don’t worry about giving answers away, good photos are worth the risk and will help others find what they are looking for.
Finally be aware of the tide and do not attempt this cache within one hour of high tide. You will get wet and it could be dangerous.
Thanks for visiting this EarthCache and I look forward to reading your logs.