I got off the train in Haymarket rather than Waverley, and as I walked into the centre of town spotted some fossils and made a quick detour for a look.

There's a few tall buildings along here, you're looking for the passageway off Morrison street, to the North side. The photo below shows you where you need to look.

1) Describe the distinctive fossil on this panel, obscured by the red rectangle. What shape is it, what colour is it? Roughly what size is it? (doesn't have to be accurate - is it as big as a fingernail/your finger/your hand will do)
2) Can you identify the fossil? - use the pictures and descriptions below to help you
3) Would your answer to question 2 be a good zone fossil? Give your reasons for this answer.
4) Take a photo of yourself at GZ, or an identifying item, being careful not to reveal any of the answers to the questions. 

Please submit your answers via message though the Geocaching website or by sending me an email - there is no need to wait for a response before logging your find.

Limestone

Limestone is a sedimentary rock formed from the remains of tiny sea creatures and shells. These remains settle on the ocean floor and build up in layers over millions of years. Over time, pressure turns these layers into solid rock. Limestone can be polished to a smooth, shiny finish and is often used for building cladding due to it's attractive appearance.

Zone Fossils in Limestone:

Zone fossils, also known as index fossils, are used to define and identify geological time periods because they are widespread, abundant, and limited to a short span of geologic time. Not all limestone fossils qualify as zone fossils, as some may not meet these criteria.

Limestone Fossils That Are Zone Fossils

Ammonite

Ammonites were marine creatures with spiral shells that lived in oceans, swimming in open waters and using gas-filled chambers for buoyancy. Especially in the Jurassic and Cretaceous periods, they are excellent index fossils due to their rapid evolution and widespread distribution.

Brachipod

A brachiopod fossil is a marine organism's shell, typically symmetrical and resembling a clam. Some species are used as zone fossils in Paleozoic limestone, such as specific Orthid and Spiriferid brachiopods.

Limestone Fossils That Aren't Zone Fossils

Gastropod

Gastropods are mollusks that lived in marine environments, using their coiled shells for protection as they crawled along the ocean floor or attached to rocks. Though present in many marine limestones, they generally evolve slowly and have broad temporal distributions, limiting their use as index fossils.

Coral

A coral fossil in limestone looks like a rough, circular pattern with ridges and grooves. Although common in limestone, many coral species have long geologic ranges, making them less useful as zone fossils.