Kris Proseus, age 11, of Lansing, Michigan, for her question:

What is shale oil?

Shales are rocky minerals of the earth's crust. They are rated as sedimentary rocks because they formed from the sediments deposited under watery lakes and seas. As a rule, they occur in flat layers somewhat like multilevel sandwiches. In their early history, these rocky deposits of shale were moist and muddy beds of clay. Time dried them out and they became hard and brittle. When shale deposits are left still longer in the earth, perhaps compressed below newer deposits, they become thin, hard sandwiches of slate.

Shallow waters often teem with small plants and populations of miniature animals. Fossilized remains of these ancient life forms were trapped in many muddy deposits of shale. In time, they were processed into hydrocarbon chemicals similar to those found in petroleum and bituminous coal. Rocks that contains such fossilized hydrocarbons are called oil bearing shales. The richest of them is called bituminous shale. It can be burned and made to yield petroleum. This so called shale oil is a tacky material ranging in color from brown to dark olive green.