The rocks that occur around Usk in central Monmouthshire were deposited in a shallow sea during the Silurian geological period just over 400 million years ago. The fossils that are found within these rocks are famous for their diversity and preservation, and this booklet acts as an introductory guide. Alfred Russell Wallace, who developed the theory of evolution alongside Charles Darwin, was born in Usk in 1823 and, although he moved away at 5 years old, it is possible that the fossils of Usk sowed a seed from which his later works grew. Simon Haslett is Professor of Physical Geography and Associate Pro Vice-Chancellor at the University of Wales. In 1988, as a student, he undertook an undergraduate geology mapping project on the Usk inlier and made notes to assist him in identifying the fossils he found. This previously unpublished booklet shares those notes along with photographs and line drawings.