The British names vitrain, clarain, and durain and the more commonly used name fusain have been adopted by the Illinois State Geological Survey as an aid in the megascopic description of the material composing the coal beds of the Illinois coal basin. Expanding activities in our laboratories in matters related to and dependent upon the physical components of our coal beds have made necessary the adoption of a technique of megascopic description that can be readily understood and easily used by both the technician and the layman. This terminology of description has not been widely used in America, but its merits are such as to inspire hope for its general adoption. To the ends that standards of usage may be established as soon as possible, the present explanation of the application of the terms to Illinois coals is advanced. The explanation requires some consideration of the original definitions of the terms and of Continental usage. The Illinois State Geological Survey has endeavored to adhere closely to the denotations of the original definitions.