Jelle Zelinga de Boer, the Harold T. Stearns Professor of Earth Science, emeritus, is the author of New Haven's Sentinels: The Art and Science of East Rock and West Rock, published by The Driftless Connecticut Series and Garnet Books in July 2013. John Wareham, video production coordinator for Information Technology Services, provided photographs for the book. East Rock and West Rock are volcanic entities that were emplaced in voluminous sandstone formations some 201 million years ago. Their presence facilitated the introduction of modern (European) geologic concepts in America by Yale University Professor Benjamin Silliman and his disciples. Furthermore, more than…