Transcriber's Note Italic text is denoted by _underscores_ and bold text by =equal signs=. Whole and partial numbers are displayed as 2-1/2. [Illustration: Photo, Ridge Studio; Courtesy Ogden Chamber of Commerce] _A great ledge in Ogden Canyon near Ogden, Utah. The rock, still retaining its stratification, was deposited layer upon layer horizontally mostly as sand upon the floor of a sea which covered the region fully 25,000,000 years ago. That the sea was of very early Paleozoic (i.e., Cambrian) age has been proved by fossils in associated strata. Long after their deep burial and consolidation within the earth, the strata were subjected to tremendous mountain-making pressure, notably altered to a rock called "Quartzite," raised high above sea level, and tilted almost vertically. Then through long ages (millions of years) overlying rocks of great thickness have been cut away (eroded) by weathering and stream action, laying bare the ledge as we see it to-day._ Popular Science Library EDITOR-IN-CHIEF GARRETT P. SERVISS AUTHORS WILLIAM J. MILLER HIPPOLYTE GRUENER A. RUSSELL BOND D. W. HERING LOOMIS HAVEMEYER ERNEST G. MARTIN ARTHUR SELWYN-BROWN ROBERT CHENAULT GIVLER ERNEST INGERSOLL WILFRED MASON BARTON WILLIAM B. SCOTT ERNEST J. STREUBEL NORMAN TAYLOR DAVID TODD CHARLES FITZHUGH TALMAN ROBIN BEACH ARRANGED IN SIXTEEN VOLUMES WITH A HISTORY OF SCIENCE, GLOSSARIES AND A GENERAL INDEX _ILLUSTRATED_ [Illustration] VOLUME THREE P. F. COLLIER & SON COMPANY NEW YORK Copyright 1922 By P. F. Collier & Son Company MANUFACTURED IN U. S. A. GEOLOGY The Science of the Earth's Crust BY WILLIAM J. MILLER Professor of Geology, Smith College [Illustration] P. F. COLLIER & SON COMPANY NEW YORK PREFACE In the preparation of this book the author has attempted to present, in popular form, the salient points of a general survey of the whole great science of geology, the science which deals with the history of the earth and its inhabitants as revealed in the rocks.