Throughout the Mesozoic and Cenozoic, tectonically activated joint fissures and karstic cave systems have acted as reservoirs for terrestrial vertebrate remains. They yield concentrations of microfaunal elements rarely if ever preserved in other situations. In the 1850s, Charles Moore realized their potential and exploited them to discover the earliest known mammals in late Triassic fissure infillings in the Carboniferous Limestone of Somerset. The history of that discovery and its associated problems of interpretation are recorded. His work greatly influenced succeeding generations of palaeontologists and, as techniques developed, fossil fissure discoveries have made a major impact on our understanding of vertebrate evolution.