Foraminifera (for-am'-in-if'-er-ah) are very small one-celled animals, commonly called "forams." They are important to geologists, who use them to identify oil-bearing rocks.
These tiny fossils are beautiful, but you will see them clearly only with the aid of a magnifying glass or hand lens. Some are calcium carbonate; others are made of tiny sand grains cemented together with silica.
Some forams make their shells from parts of the skeletons of other animals. Some are so particular about the kind of materials they use that they select only grains of a special size and color.
Forams live in tremendous numbers in the seas today. They lived as far back as the Ordovician Period, more than 400 million years ago. (The Geologic Time Chart is reproduced in the printed version of the book.)
Calcareous forams such as Endothyra (en-doh-thy'-ra) are abundant in Illinois in the Salem Limestone, which occurs in the Mississippi River bluffs along the Mc Adams Highway northwest of Alton and in the bluffs of Monroe and Randolph Counties. The Salem Limestone also crops out near Anna and Jonesboro in southern Illinois.
Another kind of calcareous foram, Fusulina (few-su-lye'-nah), is common in rocks of Pennsylvanian age throughout Illinois. The fossils look like grains of wheat and are so numerous in some limestones and shales that they can be collected by the thousands.
For a list of localities where forams are abundant, see pages 162-167 of Illinois State Geological Survey Bulletin 67.