Page 20 - Curriculum Visions Dynamic Book. To close the book, close the window or tab.

Recognising fossil corals
Corals can be found in a variety of rocks.
Some corals form reefs, and others are solitary. Sometimes, corals are broken from the reefs they grow in and their fragments are scattered among the pieces of other shells. In many cases the corals are buried in a limy mud, so that they
rarely form the whole of a rock, but
are more usually scattered within it.
Fossil corals are most commonly found in limestones. Remember that not all limestones are white. They may be grey, if they have a large mud content, and they may be stained by river water washing over them.
You can distinguish tabulate corals from rugose corals by looking for the septa (the vertical divisions within
the coral). Tabulate corals do not have septa, whereas rugose corals do. There are more major septa in hexacorals than in rugose corals.
(Left and above) You can often see fossils better if a surface has had time to be attacked by the weather. Many fossils then stand out of the matrix because they are harder and dissolve more slowly. This block of limestone is called a detrital limestone because it contains fragments (detritus) of shattered shells, corals and other fossil remains.
The inset shows a rugose coral that was spotted on the surface of the block.
By turning the block around slightly, it can be aligned with the diagram on page 18 and the septa can then be identified.
This block also contains many other fossils.
20