This article deals with a neglected passage in J. Hector St. John de Crèvecœur's unpublished writings, in which a farmer in one of the Maritime Colonies punishes one of his slaves by tying him naked to a pole in a salt meadow. Very soon after, the slave dies from an inflammation caused by mosquito bites. The article discusses the parallels and differences between this passage and the more famous slave death scene in Charleston included in the published Letters from an American Farmer. Whereas critics have argued that James's ambivalent response to the caged slave's suffering in the Charleston episode should be attributed to Crèvecœur's commitment to the dualistic ontology of modern science, this article offers an ecomaterialist reading of the salt meadow scene, revealing the presence of a competing, relational epistemology at the heart of Crèvecœur's writings. Pointing to the significance of salt in eighteenth-century natural history, in particular that of Count Buffon, the article shows how the death of the slave in the salt meadow emblematizes a broader crisis in contemporary philosophies of mechanism. The salt letter moreover brings out the ethical dilemmas attendant on this epistemological crisis in late Enlightenment natural history.