Recent years have seen the development of a more nuanced understanding of the emergence of scientific naturalism in the nineteenth century. It has become apparent that scientific naturalism did not emerge sui generis in the years following the publication of Charles Darwin’s On the origin of species (1859), but was present, if only in incipient form, much earlier in the century. Building on recent scholarship, this article adopts a geographically focused approach and explores debates about geology and phrenology— two of the diverse forms of knowledge that contributed to scientific naturalism—in lateGeorgian Belfast. Having provided the venue for John Tyndall’s infamous 1874 address as president of the British Association for the Advancement of Science, Belfast occupies a central place in the story of nineteenth-century scientific naturalism. However, in uncovering the intricate and surprising ways in which scientific knowledge gained, or was denied, epistemic and civic credibility in Belfast, this discussion will demonstrate that naturalism, materialism and the relationship between science and religion were matters of public debate in the town long before Tyndall’s intervention.