Transcriber’s Notes: Small capitals have been converted to SOLID capitals. Illustrations have been moved so they do not break up paragraphs. Typographical and punctuation errors have been silently corrected. HOW OLD ARE FOSSILS? BY SHARAT K. ROY ASSISTANT CURATOR OF INVERTEBRATE PALEONTOLOGY [Illustration] GEOLOGY LEAFLET 9 FIELD MUSEUM OF NATURAL HISTORY CHICAGO 1927 LIST OF GEOLOGICAL LEAFLETS ISSUED TO DATE No. 1. Model of an Arizona Gold Mine $ .10 No. 2. Models of Blast Furnaces for Smelting Iron .10 No. 3. Amber—Its Physical Properties and Geological Occurrence .10 No. 4. Meteorites .10 No. 5. Soils .10 No. 6. The Moon .10 No. 7. Early Geological History of Chicago .25 No. 8. Agate .50 No. 9. How old are Fossils? .25 D. C. DAVIES, DIRECTOR FIELD MUSEUM OF NATURAL HISTORY CHICAGO, U.S.A. [Illustration: LEAFLET 9. PLATE I. A VIEW OF THE GRAND CANYON OF THE COLORADO RIVER, ARIZONA. ZOROASTER IN BACKGROUND. Photograph by O. C. Farrington.] FIELD MUSEUM OF NATURAL HISTORY DEPARTMENT OF GEOLOGY CHICAGO, 1927 LEAFLET NUMBER 9 How old are Fossils? “How old is that fossil and how do you know it?” is a question frequently asked by visitors going through the hall of fossils in the Museum. A precise answer to such a question is impossible and an adequate one demands a longer time than can usually be afforded. The consequences of inadequate explanation have often proved to be unsatisfactory. The visitor becomes skeptical and instead of taking interest in the subject, he seems to be confirmed in his doubts. In this leaflet is given a condensed, general statement of methods of determining the age of ancient life. The information is drawn from the works of various authors, especially Barrell’s “Rhythms and Measurements of Geologic Time.” It is intended for those who are interested in the age of past life and yet do not intend an exhaustive study of the subject, nor have free and easy access to its literature.