Polarised light micrograph of a thin section of a Nummulitic limestone. The large coloured object is the remains of a large Nummulites sp. foraminifera. These are embedded in a fine-grained matrix of calcareous remains of smaller, planktonic organisms. This type of rock is found in South Europe and North Africa, and was deposited during the Eocene and Oligocene epochs, 37-54 million years BP (before present). Magnification: x100 when printed at 10 centimetres wide.